Bump reference/root-io-spec to c65c464 (still ROOT 6.40.04)

[sathabbott]

🤖 AI generated content

Bumps reference/root-io-spec from 9c3f776 (2026-09-18) to c65c464 (2026-09-24). It still pins ROOT 6.40.04 (1211eda), the latest stable release, so the tracked RNTuple specification (v1.0.2.1) is the same document; no code changes.

It is the first of a series of RNTuple fixes (#75, #55, #114, #49, #51, #85, #116–#122), several of which test against fixtures that only exist at the new pin:

• rntuple/compressed.root: the only compressed anchor and compressed envelopes in any corpus (scikit-hep-testdata's RNTuple anchors are all uncompressed)
• rntuple/map.root: page locators that share byte ranges
• rntuple/attributes.root: linked attribute sets, audited upstream in root-io-spec 385a3e2 with ERRATA 11–13 ([rntuple] Footer Envelope: Handle Linked Attribute Set Record Frames #51)

All three read on main today.

New expected failures. Four fixtures new since 9c3f776 fail, none of them RNTuple. Each is listed in EXPECTED_FAILURES with its exact error, per the module's rule:

Fixture	Error	Issue
classes/roofit	buffer not empty after reading object of type RooLinkedList	#71
serialization/pointer-collection	Expected a version in the StdVector header — the slot's class record followed by the content class's own frame	#105
serialization/unframed-records	TDatime / TObject / TStringLong / TQObject as records with no byte count	#123 (new), #101
written/two-versions	Grown at versions 1 and 2; the version-1 object is read with version 2's info	#22

Tests: full suite 397 passed, 61 skipped, 50 xfailed locally (was 354 passed, 53 skipped, 46 xfailed at 9c3f776). CI's non-recursive submodule checkout is unchanged.

Assisted-by: claude-code:claude-opus-5-5

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✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #124      +/-   ##
==========================================
+ Coverage   91.82%   92.16%   +0.33%     
==========================================
  Files          37       37              
  Lines        2962     2962              
==========================================
+ Hits         2720     2730      +10     
+ Misses        242      232      -10     

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[sathabbott]

@nsmith- I've reviewed and approved this, but will let you see it before it merges.

[nsmith-]

Makes sense