feat: embed commit-sealing timings in extra data

[minhd-vu]

Summary

Embed the producer's commit-sealing timings -- the same elapsed and finalize values logged by "Commit new sealing work" -- into the block's BlockExtraData, mirroring the existing TimeNano feature so the values can be read directly from the chain instead of scraped from logs.

• Add SealElapsedNano and SealFinalizeNano optional fields to BlockExtraData, plus GetSealTimings getter and SetSealTimings setter.
• Capture and embed the timings in miner commit() after FinalizeAndAssemble, gated on the Placeholder fork, rebuilding the block before sealing. The existing log line is left unchanged.
• Presence-validate both fields in verifyHeader (errMissingSealTimings); values are per-producer and non-deterministic so only presence is checked, as with TimeNano and the Giugliano fields.

Executed tests

<what was actually run beyond CI's standard unit / integration / e2e gates: kurtosis scenarios, chaos runs, manual checks against Amoy / mainnet RPCs, devnet upgrades, etc. Include output or pointers to where the run lives.>

Rollout notes

<consensus-affecting? requires coordinated upgrade? backwards-compatible? operator-facing change?>

[sonarqubecloud]

Quality Gate failed

Failed conditions
8.4% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 65.00000% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.42%. Comparing base (f1286ea) to head (296c175).

Files with missing lines	Patch %	Lines
core/types/block.go	70.96%	6 Missing and 3 partials ⚠️
miner/worker.go	0.00%	4 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (65.00%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@                          Coverage Diff                          @@
##           feature/timenano-placeholder-fork    #2277      +/-   ##
=====================================================================
- Coverage                              53.45%   53.42%   -0.04%     
=====================================================================
  Files                                    896      896              
  Lines                                 159770   159810      +40     
=====================================================================
- Hits                                   85413    85377      -36     
- Misses                                 69048    69109      +61     
- Partials                                5309     5324      +15     

Files with missing lines	Coverage Δ
consensus/bor/bor.go	85.64% <100.00%> (+0.04%)	⬆️
miner/worker.go	77.48% <0.00%> (+<0.01%)	⬆️
core/types/block.go	43.57% <70.96%> (+2.32%)	⬆️

... and 18 files with indirect coverage changes

Files with missing lines	Coverage Δ
consensus/bor/bor.go	85.64% <100.00%> (+0.04%)	⬆️
miner/worker.go	77.48% <0.00%> (+<0.01%)	⬆️
core/types/block.go	43.57% <70.96%> (+2.32%)	⬆️

... and 18 files with indirect coverage changes

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