feat: Add package data configuration and include py.typed file

[ViratiAkiraNandhanReddy]

Summary ( closes #7 )

Adds py.typed support to officially declare that caesarcipher_extended ships with inline type annotations and is compatible with PEP 561.

This improves static analysis support for users of the package and enables better integration with modern Python tooling such as type checkers, IDEs, and autocomplete systems.

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Changes

Added

• Added py.typed marker file inside:
  src/caesarcipher_extended/

Packaging

• Updated package configuration to include py.typed in built distributions

Typing Support

This allows external tools to recognize the package as typed, including:

• mypy
• Pyright
• Pylance
• other PEP 561 compatible tooling

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Why This Is Needed

Without py.typed, Python type checkers may treat the package as untyped even when inline type annotations exist.

Adding this marker:

• improves developer experience
• enables better autocomplete
• improves static analysis
• provides proper typed-package support
• aligns the project with modern Python packaging standards

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Impact

This change is non-breaking and does not affect runtime behavior.

It only improves tooling and typing metadata support for consumers of the library.

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References

• PEP 561
• Python typed package distribution standards