Add target_gas_limit to PayloadAttributes

[zilm13]

PR Description

Implementation of ethereum/consensus-specs#5235
Part of alpha.8 spec

UPDATE: feature modifies PayloadAttributesV4 adding a new field targetGasLimit. As long as Besu have not implemented it yet, we have a failing GloasUpgradeAcceptanceTest which uses real Besu, not a stub. We could either wait till it's included in some Besu release (it's not in develop yet too) or disable this test.

Fixed Issue(s)

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

Medium Risk
Changes fork-choice payload attributes and EL RPC contract on the Gloas path; mis-resolved gas limits could affect block building, though defaults and tests limit blast radius.

Overview
Adds targetGasLimit to Gloas PayloadAttributesV4 and threads it through PayloadBuildingAttributes, engine JSON-RPC, and engine_forkchoiceUpdatedV4 so the execution client receives the proposer’s desired gas limit on fork-choice updates.

ProposersDataManager now resolves targetGasLimit via ProposerPreferencesManager (slot-matched proposer gas limit), else validator registration gas limit, else zero; BeaconChainController wires the real manager into ProposersDataManager after init order is fixed.

Tests cover V4 serde, FcU v4 mapping, and gas-limit precedence. GloasUpgradeAcceptanceTest is @Disabled until Besu supports the updated payload attributes on FcU.

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[rolfyone]

mostly just a nit on the test

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[rolfyone]

that's so much better -appreciate it.

[zilm13]

GloasUpgradeAcceptanceTest is disabled, #10755 issue is created to not forget this.