Unify churn-limit helper naming to allow non-cache-requiring reuse

## Description

The churn-limit helpers in `packages/state-transition/src/util/validator.ts` have an inconsistent naming convention around whether they require an `EpochCache`:

| Function | Requires cache? |
|---|---|
| `getBalanceChurnLimit(increments, quotient, min)` | No (pure) |
| `getBalanceChurnLimitFromCache(epochCtx)` | Yes |
| `getActivationChurnLimit(epochCtx)` | Yes |
| `getExitChurnLimit(epochCtx)` | Yes |
| `getConsolidationChurnLimit(fork, epochCtx)` | Yes |
| `getActivationExitChurnLimit(epochCtx)` | Yes |

The balance-churn helper distinguishes its pure and cache-backed forms with a `FromCache` suffix, but the exit/activation/consolidation helpers exist only in cache-requiring form and take the *base* name. There is no pure `(config, increments)` counterpart for them, and the base name is already occupied by the cache version.

This came up in #9625 (Gloas `compute_weak_subjectivity_period`, EIP-8061). The plain-state weak-subjectivity path has only `(config, totalActiveBalanceIncrements)` and no `EpochCache`, so it could not reuse the existing exit/activation/consolidation helpers. To avoid the anti-pattern of constructing a fake/partial `EpochCache` cast, that PR introduced `getGloasChurnLimits(config, increments)`, which duplicates the quotient and min choices already encoded in the individual helpers.

Dependency: #9625

## Proposed change

Extract pure `(config, increments)` cores for the exit/activation/consolidation churn limits and have the cache-requiring functions delegate to them, mirroring the existing `getBalanceChurnLimit` / `getBalanceChurnLimitFromCache` split. This requires settling the naming inconsistency — either renaming the cache-taking helpers to `...FromCache` (freeing the base names for the pure cores) or an agreed alternative — which touches call sites across the Gloas processing code (exits, consolidations, registry updates), hence it was kept out of scope in #9625.

Once the pure cores exist, `getGloasChurnLimits` should be removed/reduced so the quotient/min choices live in a single place. And those functions should be called directly in the Gloas branch of weak subjectivity computation.

## Acceptance criteria

- Pure, non-cache-requiring forms exist for exit/activation/consolidation churn limits.
- Cache-requiring helpers delegate to the pure forms (single source of truth for quotients/mins).
- `getGloasChurnLimits` is removed or reduced to a thin delegator.
- Naming is consistent across the churn-limit helpers.
- Existing unit and spec tests remain green.

Start in packages/state-transition/src/util/validator.ts and review the existing cache-backed churn-limit helpers alongside getBalanceChurnLimit and getBalanceChurnLimitFromCache. Trace their call sites in the Gloas processing code and the weak-subjectivity path introduced for #9625. Done means pure forms, delegated cache forms, consistent naming, and green unit and spec tests without duplicated quotient or minimum choices.

Written by the indexing model from the issue text.