refactor(bundler): Use per-op gas calculation like Rundler

- Replace flat ENTRYPOINT_BUFFER_GAS with per-op overhead:
  - v0.6: verification_gas + 5k overhead
  - v0.7: 10k + paymaster_post_op + 1/63 (63/64ths rule)
- Add BUNDLE_SHARED_GAS (21k) for transaction intrinsic
- Add BUNDLE_TRANSACTION_GAS_OVERHEAD_PERCENT (5%) safety buffer
- Update UserOpGasInfo with paymaster fields and proper gas calculation
- Fix default aa_gas_threshold to 50% for middle-of-block bundles

Author: shamit05

crates/op-rbuilder/src/args/op.rs

@@ -100,7 +100,7 @@ pub struct OpRbuilderArgs {
     /// Threshold percentage of block gas before starting AA bundle creation (middle of block)
     #[arg(
         long = "aa.gas-threshold",
-        default_value = "30",
+        default_value = "50",
         env = "AA_GAS_THRESHOLD"
     )]
     pub aa_gas_threshold: u8,