Fix typos across codebase and documentation

[zonca]

Comprehensive typo corrections throughout the NoisePy codebase and documentation, excluding docs_old/.

Changes

Documentation (4 files, 10 typos)

• Fixed common misspellings: continous → continuous, funcionality → functionality, convinently → conveniently, paramters → parameters, overriden → overridden

Source Code (11 files, 49 typos)

Core modules:

• seis/: Fixed samping → sampling, sigularity → singularity, PARMAETERS → PARAMETERS, decomposion → decomposition, threhold → threshold
• monitoring/: Fixed strecthing → stretching, frequecies → frequencies, boolen → boolean, mesurement → measurement
• functions_2019/: Fixed flexibilty → flexibility, particuarly → particularly, startting → starting
• imaging/: Fixed tranformed → transformed, expaneded → expanded

Unchanged:
Variable names (indx, dataS, dout, padd) retained as part of codebase conventions.

Total: 59 typos fixed across 15 files with no functional changes.

Original prompt

look for typos in the entire code base and docs and make a pull request to the main branch of my own fork (zonca/NoisePy), not to the upstream repo. ignore docs_old folder.

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[niyiyu]

Thanks for correcting them. Looks nice!