upgrade python version to 3.12

[akkumar-qlik]

Description of change

(write a short description or paste a link to JIRA)

Manual QA steps

Risks

Rollback steps

• revert this branch

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Pull request overview

This PR updates the CI environment to run on Python 3.12 and adds a comprehensive new suite of unit + integration tests for the tap_codat tap (covering discovery, sync/state/bookmark behavior, HTTP client handling, and datetime transforms).

Changes:

• Update CircleCI config to use Python 3.12 and run unit tests with coverage + separate integration tests.
• Add extensive unittest-style unit tests under tests/unittests/ for core modules.
• Add mock-based integration tests under tests/ (with shared tests/base.py) and remove an older legacy test file.

Reviewed changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
.circleci/config.yml	Switch CI to CircleCI 2.1, Python 3.12 venv, run unit tests w/ coverage + run integration tests.
tests/base.py	Introduce shared mock API data + helpers for integration tests.
tests/test_all_fields.py	Integration coverage validating full field replication across streams using mock responses.
tests/test_automatic_fields.py	Integration coverage validating all discovered fields are marked inclusion=automatic.
tests/test_bookmark.py	Integration coverage for bookmark/state behavior during incremental syncs.
tests/test_discovery.py	Integration coverage for discovery output correctness (streams, keys, schema).
tests/test_pagination.py	Integration coverage for pagination behavior with mocked responses.
tests/test_start_date.py	Integration coverage for start_date behavior in incremental vs full-table streams.
tests/test_sync.py	End-to-end integration tests for sync() and CLI entrypoint behaviors.
tests/test_sync_canary.py	Canary integration tests to ensure the pipeline emits schemas/records.
tests/unittests/__init__.py	Make tests/unittests importable as a package.
tests/unittests/test_client.py	Unit tests for HTTP client URL building and response handling.
tests/unittests/test_discover.py	Unit tests for discovery helpers, catalog metadata, and stream configuration.
tests/unittests/test_init.py	Broad unit tests covering multiple modules (state/transform/http/context/discover/sync).
tests/unittests/test_state.py	Unit tests for state load/save/incorporation and bookmark parsing.
tests/unittests/test_sync.py	Unit tests for Context, stream sync helpers, formatting, and main sync behavior.
tests/unittests/test_transform.py	Unit tests for datetime path discovery + transformation utilities.
test/test_report_flattening.py	Remove legacy flattening test under the old test/ path.

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[mukeshbhatt18gl]

it should be tap-tester

[RushiT0122]

Approved but please fix changelog as suggested before merging.