core: start gloas attester consensus at slot start

[KaloyanTanev]

From the gloas fork, attester consensus starts at the start of the slot with the new eager_ahead_split timer (rounds of 4s, 1s, 1s, then +1s per round, extend_on_rearm_1s), and the fetcher fetches attestation data on the slot's SSE head event, or at the attestation deadline if no block arrived. fetch_att_on_block becomes stable and fetch_att_on_block_with_delay is removed. Stacked on #4767.

category: feature
ticket: #4324

[codecov]

Codecov Report

❌ Patch coverage is 89.18919% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.95%. Comparing base (58e30cc) to head (bc51f45).

Files with missing lines	Patch %	Lines
core/fetcher/fetcher.go	93.33%	4 Missing ⚠️
app/app.go	0.00%	3 Missing ⚠️
core/scheduler/scheduler.go	76.92%	3 Missing ⚠️
core/consensus/qbft/qbft.go	66.66%	1 Missing ⚠️
core/interfaces.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                      Coverage Diff                      @@
##           kalo/round-timer-refactor    #4769      +/-   ##
=============================================================
+ Coverage                      66.76%   66.95%   +0.18%     
=============================================================
  Files                            250      250              
  Lines                          32289    32377      +88     
=============================================================
+ Hits                           21559    21677     +118     
+ Misses                         10729    10699      -30     
  Partials                           1        1              

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[sonarqubecloud]

Quality Gate passed

Issues
14 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Copilot]

🟡 Changes recommended

Sequential callbacks delay consensus participation, while timing races can miss or postpone head-event fetching.

4 open findings

• Fixed timer interval ignores network slot duration · New
• Fetching blocks consensus participation at slot start · New
• Head events are dropped before waiter registration · New
• Per-event Spec request delays latency-critical delivery · New

What changed in this PR

Adds Gloas-specific attester timing so consensus can begin at slot start and fetch attestation data from SSE head events.

Changes:

• Adds the eager_ahead_split consensus timer.
• Adds head-event fetching with deadline fallback.
• Stabilizes fetch_att_on_block and expands tests/documentation.

File	Description
app/​app.go	Wires Gloas head events into the fetcher.
app/​featureset/​featureset.go	Stabilizes and consolidates attestation fetching flags.
core/​consensus/​qbft/​qbft.go	Supplies fork timing to round timers.
core/​consensus/​qbft/​qbft_internal_test.go	Updates timer construction tests.
core/​consensus/​qbft/​roundtimer_internal_test.go	Tests Gloas rounds in QBFT.
core/​consensus/​timer/​extensions.go	Adds per-round rearm extension behavior.
core/​consensus/​timer/​roundtimer.go	Selects fork-aware timers and anchors.
core/​consensus/​timer/​roundtimer_internal_test.go	Tests durations, anchors, and extensions.
core/​consensus/​timer/​roundtimer_test.go	Tests fork-aware timer selection.
core/​consensus/​timer/​timers.go	Defines the ahead-split timer.
core/​fetcher/​fetcher.go	Implements Gloas head-event fetching and fallback.
core/​fetcher/​fetcher_internal_test.go	Tests the new fetching flow.
core/​fetcher/​fetcher_test.go	Updates fetcher construction.
core/​interfaces.go	Annotates legacy pre-Gloas wiring.
core/​scheduler/​scheduler.go	Starts Gloas attester duties at slot start.
core/​scheduler/​scheduler_internal_test.go	Tests fork-aware head handling.
core/​scheduler/​scheduler_test.go	Tests Gloas scheduling without offset delay.
docs/​consensus.md	Documents Gloas timer semantics.
testutil/​integration/​simnet_test.go	Adds Gloas attester integration coverage.

🧠 Review effort: Balanced

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