Generate and verify shared serial layouts without enabling production routes

[swackhamer]

ExifTool serial layouts were inventoried but could not run through a shared Rust reader. This change generates descriptors from the pinned native source, adds a bounded reader, and verifies emitted artifacts independently. It prepares Real AudioV4 to replace its copied field sequence in a separate change.

All eight native tables remain accounted for: 130 entries / 132 alternatives, with 106 emitted alternatives and 26 explicit omissions. Unsupported tables remain disabled; this PR enables no production caller and claims no manual-reader retirement or new autogenerated percentage.

The standard regeneration manifest, write guard, CI and table verification now include the serial artifact. Independent checks reject missing or forged table/row omissions and authenticate native group defaults. Real AudioV3/V4 replay compares actual generated-table reads with pinned native callbacks; final metadata grouping and other unexercised behavior remain documented limits.

Validation:

• 64 focused Python tests pass with no failures or skips.
• 13 shared-reader Rust unit tests pass.
• The explicit native/Rust integration test passes ten cases on threaded and non-threaded Perl 5.38.2 against pinned ExifTool 13.59; CI requires one passed test to reject an empty selector.
• Full Clippy with all features and warnings denied, plus formatting, pass.
• Official regeneration passes for all 32 declared artifacts. Generated Rust is unchanged; the expression ledger also reproduces exactly with the portable producer invocation. All 607 expressions pass 16,789 applicable native comparisons; 14 probe inputs are inapplicable.

Full hosted acceptance passed at 72fbebb1: all five required checks succeeded. Canonical Python passed 757 tests with no failures/skips in 641.913 seconds. Nextest passed 5,756 tests (59 intentionally skipped), the complete Cargo test/doc invocation passed, and the explicitly invoked serial native replay passed. Benchmarks were intentionally skipped. The checkpoint and updated plan distinguish source inventory, executable proof, production activation, and remaining carrier/corpus/upgrade checks.