Keep interior comments in empty flow collections

[BetterAndBetterII]

Empty flow collections were dropping interior comments (FootComment with empty content). Hold that comment as HeadComment so it survives emit.

Fixes #406

[Copilot]

🟢 Approval recommended

The emitter change is narrowly scoped, addresses the described failure mode for empty flow collections, and is backed by new regression tests covering the reported cases.

Pull request overview

Fixes emission of interior comments for otherwise-empty flow collections ({} / []) by preventing the START-event FootComment from being flushed before the opening bracket is written, keeping the comment inside the collection as intended (per #406).

Changes:

• Reclassify START-event FootComment as HeadComment for empty flow sequences/mappings so it isn’t emitted before [/{.
• Ensure flow sequences also flush any pending HeadComment when emitting the closing ] (covers the empty-sequence case with no items to trigger comment processing).
• Add targeted regression coverage in both emitter.yaml and a Go unit test that validates bracket/comment ordering and re-parsability.

File summaries

File	Description
internal/libyaml/emitter.go	Holds interior comments for empty flow collections and emits them inside brackets; adds sequence-end head-comment flush.
internal/libyaml/testdata/emitter.yaml	Adds roundtrip regression cases covering empty flow mapping/sequence comment placement scenarios from #406.
internal/libyaml/emitter_test.go	Adds a focused unit test ensuring the emitted YAML keeps the comment between the opening and closing brackets and remains parseable.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 0
• Review effort level: Lite

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[ccoVeille]

Sounds good. Thanks for working on this