in fetch.get_interval, make sure db is closed

[javierggt]

Description

This PR fixes a warning that appears in python 3.13 (ska3-hope).

This is the warning:

cheta/cheta/tests/test_comps.py::test_quat_comp_bad_times
  /Users/javierg/miniforge3/envs/ska3-flight-2026.0rc4/lib/python3.13/site-packages/_pytest/unraisableexception.py:67: PytestUnraisableExceptionWarning: Exception ignored in: <sqlite3.Connection object at 0x12da75c60>
  
  Traceback (most recent call last):
    File "<frozen importlib._bootstrap_external>", line 781, in _compile_bytecode
  ResourceWarning: unclosed database in <sqlite3.Connection object at 0x12da75c60>

The cause for the warning is a Ska.DBI instance that seems to be kept alive inside a cached result. Somehow a reference to the db is attached to the cached result even if it is not necessary, and at exit the connection is still open.

The fix in this PR is to explicitly close it by using the context manager.

Interface impacts

Testing

Unit tests

• Linux

(ska3-flight-2026.0rc4) jgonzale cheta $ git rev-parse HEAD
fccd7ff016f6d034c601d3915a01545a248ae84b
(ska3-flight) jgonzale cheta $ pytest cheta
==================================================================== test session starts =====================================================================
platform linux -- Python 3.12.8, pytest-8.3.4, pluggy-1.5.0
rootdir: /proj/sot/ska/jgonzalez/git
configfile: pytest.ini
plugins: anyio-4.7.0, timeout-2.3.1
collected 187 items                                                                                                                                          

cheta/tests/test_comps.py .............ss.......................................................                                                       [ 37%]
cheta/tests/test_data_source.py ...........                                                                                                            [ 43%]
cheta/tests/test_fetch.py .................................                                                                                            [ 60%]
cheta/tests/test_intervals.py .........................                                                                                                [ 74%]
cheta/tests/test_orbit.py .                                                                                                                            [ 74%]
cheta/tests/test_remote_access.py ......                                                                                                               [ 78%]
cheta/tests/test_sync.py ........                                                                                                                      [ 82%]
cheta/tests/test_units.py ...........                                                                                                                  [ 88%]
cheta/tests/test_units_reversed.py ...........                                                                                                         [ 94%]
cheta/tests/test_utils.py ...........                                                                                                                  [100%]

====================================================================== warnings summary ======================================================================
cheta/cheta/tests/test_comps.py::test_cmd_states
  /export/jgonzale/miniconda3/envs/ska3-flight/lib/python3.12/site-packages/setuptools_scm/git.py:312: UserWarning: git archive did not support describe output
    warnings.warn("git archive did not support describe output")

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=================================================== 185 passed, 2 skipped, 1 warning in 167.95s (0:02:47) ====================================================
(ska3-flight) jgonzale cheta $ conda activate ska3-flight-2026.0rc4
(ska3-flight-2026.0rc4) jgonzale cheta $ pytest cheta
==================================================================== test session starts =====================================================================
platform linux -- Python 3.13.10, pytest-9.0.1, pluggy-1.6.0
rootdir: /proj/sot/ska/jgonzalez/git
configfile: pytest.ini
plugins: timeout-2.4.0, anyio-4.12.0
collected 187 items                                                                                                                                          

cheta/tests/test_comps.py .............ss.......................................................                                                       [ 37%]
cheta/tests/test_data_source.py ...........                                                                                                            [ 43%]
cheta/tests/test_fetch.py .................................                                                                                            [ 60%]
cheta/tests/test_intervals.py .........................                                                                                                [ 74%]
cheta/tests/test_orbit.py .                                                                                                                            [ 74%]
cheta/tests/test_remote_access.py ......                                                                                                               [ 78%]
cheta/tests/test_sync.py ........                                                                                                                      [ 82%]
cheta/tests/test_units.py ...........                                                                                                                  [ 88%]
cheta/tests/test_units_reversed.py ...........                                                                                                         [ 94%]
cheta/tests/test_utils.py ...........                                                                                                                  [100%]

====================================================================== warnings summary ======================================================================
cheta/cheta/tests/test_comps.py::test_cmd_states
  /export/jgonzale/miniconda3/envs/ska3-flight-2026.0rc4/lib/python3.13/site-packages/setuptools_scm/git.py:427: UserWarning: git archive did not support describe output
    warnings.warn("git archive did not support describe output")

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=================================================== 185 passed, 2 skipped, 1 warning in 178.66s (0:02:58) ====================================================

Independent check of unit tests by [REVIEWER NAME]

• [PLATFORM]:

Functional tests

No functional testing.