perf(erpc:PLA-692): partial multicall fallback and terminal handling

[0x666c6f]

Summary

• Reduce multicall fallback amplification in eth_call batch aggregation.
• Retry only failed subcalls while preserving successful multicall subresults.

Changes

• retry failed decoded multicall3 subcalls individually (partial fallback)
• keep successful decoded subcalls as direct multicall results (no re-forward)
• treat terminal multicall response corruption paths as terminal errors (no full fallback re-forward)
• classify multicall RPC errors into recoverable (fallback) vs terminal (no fallback)
• add fallback-reason matrix metric:
  • erpc_multicall3_fallback_reason_matrix_total{reason,mode}
  • mode: full|partial|terminal
• wire erpc_multicall3_fallback_requests_total{outcome} in fallback worker path
• update aggregation/fallback regression tests for new behavior

Linear

• PLA-692: https://linear.app/morpho-labs/issue/PLA-692/erpc-optimize-eth-call-fallback-partial-retry-avoid-double-forward

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 6501b5fa26

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".