refactor(build): Simplify git metadata collection code (EME-604)

Extract git metadata collection logic into a separate function and struct
to improve code readability. The large if/else block in execute() is now
just 5 lines instead of ~189 lines.

Also remove the --no-git-metadata flag, keeping only --git-metadata with
true/false values for consistency.

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Co-Authored-By: Claude <[email protected]>

Author: runningcode