fix: correct tx gas limit cap check (Osaka / EIP-7825)

[sashaodessa]

Summary

Enforce the transaction gas limit cap only when explicitly enabled.

What changed

• Replaced is_none() with is_some() in:
  • crates/anvil/src/eth/backend/mem/mod.rs
  • crates/anvil/src/eth/backend/executor.rs

Why

• The previous logic inverted the check, causing the cap to not be enforced when configured.
• Aligns validation/execution with Osaka (EIP-7825) expectations and prevents oversized txs slipping through.

[onbjerg]

this is incorrect.

[sashaodessa]

@onbjerg but you approved this #11783