Add local exercise repo fetching for testing local changes

[VikramGoyal23]

Allows developers to set the exercise source as a local path, enabling fully local exercise testing. Backwards compatible and assumes lack of type field as remote.

[Copilot]

Pull request overview

This pull request adds support for using local exercise repositories for testing, enabling developers to test exercise changes locally before pushing to remote. The implementation maintains backwards compatibility by defaulting to "remote" type when the type field is absent.

Changes:

• Extended ExercisesSource dataclass to support both "remote" and "local" repository types with appropriate fields for each
• Added from_raw class method for flexible deserialization with backwards compatibility
• Implemented local repository copying logic using shutil.copytree for isolation

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

File	Description
app/configs/gitmastery_config.py	Extended ExercisesSource to support local/remote types, added from_raw factory method for backwards-compatible deserialization
app/utils/gitmastery.py	Added local repo handling branch in enter method with path validation and directory copying logic

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[jovnc]

@VikramGoyal23 Is this ready for review? Would also be good to resolve copilot comments if they have been addressed as well to reduce cognitive load on reviewer

[VikramGoyal23]

@jovnc Yes, this is ready for another review

[jovnc]

@VikramGoyal23 This is more of an experimental change, so we will leave it here for now, and merge in during later weeks (or when E2E tests are ready) to prevent unnecessary regressions.