feat(spice): certified accumulator ordinal index + inclusion proofs

[darioush]

Adds the canonical per-ordinal index over the certified accumulator and the light-client inclusion-proof generation anchored to it.

• Two columns: CertifiedAccumulatorByOrdinal (ordinal -> frontier-before-leaf + leaf hash) and CertifiedBlockLeafOrdinal (block -> ordinal).
• index_canonical_certified_leaves: re-points the ordinal index along the canonical chain only (from postprocess_block when the block is canonical, and from update_height's reorg walk), so orphaned forks can't pollute proofs.
• compute_certified_block_proof (reusing the shared compute_merkle_path_by_ordinal helper) and Chain::spice_block_header_lite_and_proof.

Testing

• test_certified_block_proof_unaffected_by_side_fork: a losing fork re-certifies a block with different roots; the canonical proof still verifies.
• test_certified_block_proof_follows_reorg: a heavier fork wins and the ordinal index re-points; a proof against the new head verifies against the fork's root and differing leaf.

5/6 of the SPICE light-client stack (#15947). Base: #15965.

[codecov]

Codecov Report

❌ Patch coverage is 86.15385% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.53%. Comparing base (bb0b522) to head (4824613).

Files with missing lines	Patch %	Lines
chain/chain/src/chain.rs	61.11%	0 Missing and 7 partials ⚠️
chain/chain/src/store/mod.rs	92.06%	2 Missing and 3 partials ⚠️
chain/chain/src/chain_update.rs	77.77%	1 Missing and 1 partial ⚠️
chain/chain/src/spice/certified_accumulator.rs	81.81%	1 Missing and 1 partial ⚠️
core/store/src/columns.rs	85.71%	2 Missing ⚠️

Additional details and impacted files

@@                           Coverage Diff                           @@
##           darioush/spice-lc-commit-validate-4   #15966      +/-   ##
=======================================================================
+ Coverage                                72.52%   72.53%   +0.01%     
=======================================================================
  Files                                      947      947              
  Lines                                   204612   204741     +129     
  Branches                                204612   204741     +129     
=======================================================================
+ Hits                                    148396   148518     +122     
+ Misses                                   51235    51229       -6     
- Partials                                  4981     4994      +13     

Flag	Coverage Δ
pytests-nightly	1.10% <0.00%> (-0.01%)	⬇️
unittests	69.34% <1.69%> (-0.04%)	⬇️
unittests-nightly	69.32% <1.69%> (-0.04%)	⬇️
unittests-spice	66.92% <87.50%> (+0.01%)	⬆️

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