refactor(source-map): scope pending construct spans

[luojiyin1987]

What changed

• Move the pending construct span out of RecordingState.
• Consume each pending span through one guarded function.
• Reject missing or overlapping pending constructs.
• Cover consecutive and alternating constructs.

Why

Raw activeStart and activeEnd fields could remain after their event. One typed pending value makes the enter and exit pairing explicit.

Impact

RecordingState now contains only persistent recording maps. Parser output and source-map behavior stay unchanged.

Checks

• 1,852 source-map tests passed.
• Full pnpm run prepublishOnly passed.
• 14 test suites passed.
• 1,956 tests passed.
• Build, type tests, ESLint, and package checks passed.

Closes #85
Part of #86

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