chore: merge unstable into epbs (CI check only, do not squash)

[shane-moore]

Merges unstable into epbs as a true merge commit, bringing in the 12 commits epbs is behind, including the ruint 1.20.0 bump (#1202) that fixes the cargo audit failure currently breaking epbs-based PR CI (e.g. #1215).

Do not merge via GitHub (squash would break the eventual epbs -> unstable merge). This PR exists only to run CI against the merge result; once green it will be closed and the identical merge commit pushed directly to epbs, matching the existing pattern on that branch (b162b606, a9f378a4).

Conflict resolutions:

• Cargo.toml: kept the epbs lighthouse pin (81d576943); unstable's v8.2.1 pin lacks Gloas types.
• Cargo.lock: rebuilt from unstable's side (preserves ruint 1.20.0), then reconciled so all 31 lighthouse crates are back on 81d576943.
• .github/custom/local-testnet/params.yaml: took unstable's lighthouse v8.2.1 image bump.
• validator_store/src/lib.rs: kept epbs's refactor (decide_committee_vote, round_deadline_origin); it already contains unstable's get_slot_duration() cleanup. The fix: harden signature reconstruction #1198 validator_pubkey signing-data change auto-merged.
• validator_store/src/testing/common.rs: union of epbs's hang/failure mock and fix: harden signature reconstruction #1198's validator_pubkey capture (asserted by the committee_attestation test).

cargo check --workspace --all-targets passes on the merge.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 82.87293% with 62 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (epbs@7bad23f). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
anchor/signature_collector/src/lib.rs	77.51%	47 Missing ⚠️
anchor/network/src/behaviour.rs	68.18%	7 Missing ⚠️
anchor/network/src/network.rs	0.00%	3 Missing ⚠️
anchor/client/src/lib.rs	0.00%	2 Missing ⚠️
anchor/network/src/discovery.rs	96.66%	2 Missing ⚠️
anchor/subnet_service/src/topic.rs	97.82%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             epbs    #1216   +/-   ##
=======================================
  Coverage        ?   69.67%           
=======================================
  Files           ?      165           
  Lines           ?    32475           
  Branches        ?        0           
=======================================
  Hits            ?    22626           
  Misses          ?     9849           
  Partials        ?        0           

Flag	Coverage Δ
rust	69.67% <82.87%> (?)

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