feat(cli): add create-tests command for autogenerating unit test stubs (#74)

[AlexandruAchilleF]

Closes #74

Adds a new CLI command create-tests to automatically generate pytest-style unit test stubs for Hamilton functions in a specified module.

Changes

• Implemented create_test_stubs and AST/signature inspect helpers in hamilton/cli/logic.py to scan functions and construct unit test stubs.
• Added parameter default value generation, type hints propagation, and expected assertions (with specialized support for pandas Series/DataFrames).
• Preserves existing test files by appending only missing tests and skipping already implemented function tests.
• Exposed create_tests in hamilton/cli/commands.py and registered the Typer command in hamilton/cli/__main__.py.
• Added automated unit tests in tests/cli/test_logic.py.

How I tested this

• Ran pytest tests/cli/test_logic.py locally (all 4 tests passed).
• Manually verified CLI generation using a sample flow file and confirmed idempotent behavior (no duplicate stubs added on subsequent runs).

Notes

N/A

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.