feat: support built-in log formats

[liyimil]

What changed

• accept Git's oneline, short, medium, full, and fuller log format presets
• map each preset to structured result fields
• expose format-aware TypeScript return types
• add a changeset and regression coverage for the fuller preset

Why

git.log({format: 'fuller'}) was previously treated like the default object format instead of the corresponding built-in Git pretty format. This adds the string shortcut while retaining the existing custom format object behavior.

Fixes #883.

Checks

• yarn workspace simple-git jest --runInBand test/unit/log.spec.ts (43 tests passed)
• yarn tsc -p simple-git/tsconfig.release.json --noEmit
• Biome check for all changed files
• git diff --check

The full suite also ran: 767 tests passed; 21 unrelated integration tests failed on Windows because they depend on POSIX shell commands/path separators, external clone authentication, or timing-sensitive process behavior.

Prepared with Codex assistance; the diff was reviewed and the checks above were run locally.

[changeset-bot]

🦋 Changeset detected

Latest commit: f726f24

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
simple-git	Minor

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