docs: rewrite iso2709 + reader comments in declarative terms

[dchud]

Summary

Source comments and module docs should describe what the code does and why in timeless terms, not the implementation process that produced them. Earlier comments referenced specific PR identifiers, "the error-enrichment work" (a forward reference to in-progress work on a related bead), and "Currently extracted / Not yet extracted" framing — all of which become noise or actively misleading once the related work lands.

Changes

• src/iso2709.rs module docstring: replace "Currently / Not yet" framing with a single declarative description of what's in the module and what stays in each reader (and why)
• src/reader.rs, src/authority_reader.rs, src/holdings_reader.rs: replace three identical comment blocks referencing a specific PR with a single declarative note that the recovery dispatch is unreachable in practice because the read primitive returns a buffer of full length

No code changes; doc-only.

Test plan

• .cargo/check.sh --quick clean locally
• Pre-commit hook ran the check on commit
• CI green on all platforms

🤖 Generated with Claude Code

[codspeed-hq]

Merging this PR will degrade performance by 11.91%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

❌ 2 (👁 2) regressed benchmarks
✅ 58 untouched benchmarks
⏩ 16 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
👁	WallTime	test_process_4_files_parallel_4_threads	89.2 ms	101.3 ms	-11.91%
👁	WallTime	test_process_8_files_parallel_4_threads	196.9 ms	221.3 ms	-11.01%

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_{Comparing chore/iso2709-comments-cleanup (6a474d2) with main (8129ac4)}

Footnotes

1. 16 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩