feat: implement compute_weak_subjectivity_period for Gloas (EIP-8061)

[markolazic01]

Motivation

Implements the Gloas compute_weak_subjectivity_period (modified in EIP-8061),
which the weak-subjectivity guide updated to weight churn asymmetrically.
Resolves the gap left by #9305, which implements EIP-8061.

Description

• Add computeWeakSubjectivityPeriodFromConstituentsGloas, following the
  Phase0/Electra FromConstituents pattern (caller supplies pre-computed churn
  limits; function does only the period math).
• Assemble delta per spec: 2/3 * exit + 1/3 * activation + consolidation,
  flooring each weighted term independently, then apply the increment→Gwei
  scaling as the Electra path does.
• Gate Gloas ahead of Electra in both computeWeakSubjectivityPeriod and
  computeWeakSubjectivityPeriodCachedState (Gloas is post-Electra, so the
  order matters).
• Add getGloasChurnLimits helper for the plain-state path, which has no
  EpochCache to hand the existing epochCtx-based churn helpers.
• Register compute_weak_subjectivity_period#gloas in specrefs (remove the
  alpha.3 "not yet implemented" exception, point it at the implementation).
• Add unit tests with expected periods derived independently from the spec's
  integer Gwei arithmetic, covering the exit MIN floor, the activation cap, and
  the exit/activation asymmetry EIP-8061 introduces.

Closes #9337

• getGloasChurnLimits is called before the fork specific computeWeakSubjectivity calls for readability, it also runs on pre-Gloas forks but is negligible.
• getGloasChurnLimits is a function made due to reasons of existing naming entanglement:
  getBalanceChurnLimit -> requires no epoch cache
  getBalanceChurnLimitFromCache -> requires cache
  getActivationChurnLimit(and other wrappers) -> require cache
  This didn't allow for elegant creation of 'non-cache-requiring' wrappers or helpers, and that is why the most elegant solution seemed to be getGloasChurnLimits.

This topic should be addressed in another PR, I'll open a follow-up issue for it.

AI Assistance Disclosure

• External Contributors: I have read the contributor guidelines and disclosed my usage of AI below.

Used Claude to navigate the repo, review the diffs, and derive/verify the unit test values; it also drafted parts of this description. All code was authored and applied manually.

[gemini-code-assist]

Warning

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[markolazic01]

/gemini review

[gemini-code-assist]

Code Review

This pull request implements the weak subjectivity period calculation for the Gloas fork, introducing getGloasChurnLimits and computeWeakSubjectivityPeriodFromConstituentsGloas along with corresponding unit tests and spec reference updates. The review feedback suggests optimizing computeWeakSubjectivityPeriod by moving the getGloasChurnLimits call inside the Gloas-specific conditional block. This prevents unnecessary execution and potential NaN errors on older forks where Gloas configuration parameters might not be defined.

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[gemini-code-assist]

Currently, getGloasChurnLimits is called unconditionally, even for pre-Gloas forks. If Gloas configuration parameters (like CHURN_LIMIT_QUOTIENT_GLOAS) are not defined or initialized on older forks or certain networks, this will result in NaN values being computed and passed around, which is unnecessary and potentially error-prone. Moving this calculation inside the isForkPostGloas(fork) conditional block ensures it is only executed when actually needed.

  if (isForkPostGloas(fork)) {
    const churnLimitsGloas = getGloasChurnLimits(config, totalActiveBalanceIncrements);
    return computeWeakSubjectivityPeriodFromConstituentsGloas(
      totalActiveBalanceIncrements,
      churnLimitsGloas.exit,
      churnLimitsGloas.activation,
      churnLimitsGloas.consolidation,
      config.MIN_VALIDATOR_WITHDRAWABILITY_DELAY
    );
  }

  return isForkPostElectra(fork)
    ? computeWeakSubjectivityPeriodFromConstituentsElectra(
        totalActiveBalanceIncrements,
        getBalanceChurnLimit(
          totalActiveBalanceIncrements,
          config.CHURN_LIMIT_QUOTIENT,
          config.MIN_PER_EPOCH_CHURN_LIMIT_ELECTRA
        ),
        config.MIN_VALIDATOR_WITHDRAWABILITY_DELAY
      )
    : computeWeakSubjectivityPeriodFromConstituentsPhase0(
        activeIndices.length,
        totalActiveBalanceIncrements,
        getChurnLimit(config, activeIndices.length),
        config.MIN_VALIDATOR_WITHDRAWABILITY_DELAY
      );

[markolazic01]

Noted this in the PR desc, it is not perfect but it is imo harmless and much more readable as is.
Willing to change this if needed ofc.