Containers and config for non-validating staked builders

[StefanBratanov]

PR Description

Containers and config as per ethereum/consensus-specs#4788

Even though yet not merged, specs have been more or less approved, so I don't expect changes in the structures, so it's a good start to prepare for this change.

Specrefs CI is supposed to fail, will fix after new release of consensus-specs

Fixed Issue(s)

N/A

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

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Note

Prepares Gloas for non-validating staked builders with new containers, state fields, and configuration.

• Adds Builder SSZ container and exposes builders list and next_withdrawal_builder_index in BeaconStateGloas; updates schema indices and state accessors/mutators
• Wires new config: BUILDER_REGISTRY_LIMIT, MIN_BUILDER_WITHDRAWABILITY_DELAY, MAX_BUILDERS_PER_WITHDRAWALS_SWEEP; extends SpecConfigGloas, builder, impl, and presets/yamls; fixes zero default for Long in SpecBuilderUtil
• Moves BuilderPendingPayment/BuilderPendingWithdrawal under state.versions.gloas and updates schema registry and usages
• Initializes new fields during Gloas state upgrade; retains withdrawal sweep logic alignment
• Extends REST API schemas (BeaconStateGloas.json, new Builder.json) and updates mainnet config fixture
• Adds property tests and test suppliers/builders for new types

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