Use sync.Pool for keccak state

[cffls]

Description

Use sync.Pool in Keccak hash operations to reduce memory allocations and GC pressure.

Performance impact:

• Reduced GC pressure: scanobject decreased from 20.43% to 2.59%
• Improved memory management: mallocgc reduced to 1.52% (7.38% cumulative)
• More efficient state operations with less GC overhead
• Transaction processing shows improved efficiency with less GC interference

While the core Keccak hash computation (keccakF1600) still takes 11.75% CPU time, the overall system performance has improved due to reduced memory allocation overhead and better GC characteristics.

pprof before

pprof after

Changes

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Changes only for a subset of nodes

Checklist

• I have added at least 2 reviewer or the whole pos-v1 team
• I have added sufficient documentation in code
• I will be resolving comments - if any - by pushing each fix in a separate commit and linking the commit hash in the comment reply
• Created a task in Jira and informed the team for implementation in Erigon client (if applicable)
• Includes RPC methods changes, and the Notion documentation has been updated

Cross repository changes

• This PR requires changes to heimdall
  • In case link the PR here:
• This PR requires changes to matic-cli
  • In case link the PR here:

Testing

• I have added unit tests
• I have added tests to CI
• I have tested this code manually on local environment
• I have tested this code manually on remote devnet using express-cli
• I have tested this code manually on mumbai/amoy
• I have created new e2e tests into express-cli

[pratikspatil024]

Noice!