Fix getLightClientProofByL1Height to use hex serialized alloy::U64

[Copilot]

The getLightClientProofByL1Height RPC method was using a regular u64 parameter instead of hex-serialized alloy::U64, making it inconsistent with other RPC methods in the codebase and Ethereum JSON-RPC standards.

Changes Made

• Added alloy_primitives::U64 import to the light client prover RPC module
• Updated the trait method signature from l1_height: u64 to l1_height: U64
• Updated the implementation to convert U64 to u64 using the .to() method when calling the database layer
• Ensured compatibility with existing test code through automatic type conversion

Before

async fn get_light_client_proof_by_l1_height(
    &self,
    l1_height: u64,  // Plain u64 - no hex serialization
) -> RpcResult<Option<LightClientProofResponse>>;

After

async fn get_light_client_proof_by_l1_height(
    &self,
    l1_height: U64,  // alloy::U64 - proper hex serialization
) -> RpcResult<Option<LightClientProofResponse>>;

This change ensures the method follows the same pattern as other RPC methods like get_sequencer_commitments_on_slot_by_number, get_verified_batch_proofs_by_slot_height, and get_l2_block_by_number, which all use alloy_primitives::U64 for height parameters to provide proper JSON-RPC hex serialization (e.g., "0x1a2b" instead of decimal 6827).

Fixes #2509.

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