Separate precompile gas cost calculation and runtime implementation

[goodlyrottenapple]

Depends on #2098

More prep-work for zkVM compilation. This will allow us to conditionally compile precompiles_impl.cpp for x86 only and supply an alternative precompiles_impl.cpp for the different zkVMs, whilst always compiling precompiles_gas_cost_impl.cpp for all targets.

[Copilot]

Pull request overview

This PR refactors precompile logic to separate gas cost calculation from runtime execution, enabling gas-cost code to be built for all targets (including zkVM guests) while leaving execution implementations target-specific (e.g., x86-only).

Changes:

• Introduces dedicated gas-cost implementation TUs for Ethereum and Monad precompiles.
• Removes gas-cost logic from precompiles_impl.cpp, leaving it focused on execution/runtime.
• Updates category/execution/CMakeLists.txt to compile the new gas-cost implementation files.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
category/execution/monad/monad_precompiles_gas_cost_impl.cpp	Adds Monad-specific precompile gas-cost implementations (pricing-factor adjusted).
category/execution/ethereum/precompiles_impl.cpp	Removes gas-cost helpers/templates from the runtime execution implementation file.
category/execution/ethereum/precompiles_gas_cost_impl.cpp	Adds Ethereum precompile gas-cost implementations previously embedded in precompiles_impl.cpp.
category/execution/CMakeLists.txt	Wires new gas-cost implementation files into the build.

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