feat(codegen): solc-shaped internal helper outlining for Yul identity targets

Context

Morpho Midnight Yul identity is now gated by python3 scripts/report_yul_identity_gap.py --midnight --enforce-configured-gate in the downstream morpho-verity workspace.

Current report shape, from out/parity-target/morpho-midnight/report.json on the c3bed0e Verity pin:

• hashMismatch: 0
• onlyInSolidity: 75
• onlyInVerity: 226
• Largest onlyInVerity surface: 180 internal_internal_*/modifier helper functions, generally duplicated as #0 and #1
• Additional Verity-only helper surface: 44 __verity_*_checked ABI bounds helpers and 2 mappingSlot helpers

Feature request

Add a Yul identity/codegen mode that can outline or inline internal Verity helper functions in a solc-shaped way for Solidity parity targets. The target behavior is to reduce or eliminate the internal_internal_*/modifier-only helper family drift when a Verity contract is intended to mirror a Solidity irOptimized artifact.

This could be implemented as one or more of:

• A lowering pass that inlines simple internal helpers and modifiers when solc would not emit a distinct function block.
• A helper naming/outline policy that intentionally matches solc helper block structure for internal functions when equivalent.
• A reportable metadata mode that separates compiler-introduced helper blocks from semantic contract functions, if exact structural convergence is not feasible.

Why this matters

This is the largest remaining Midnight function-level identity category. It is not a semantic parity failure, but it keeps the downstream Yul identity gate manifest large and prevents the Solidity and Verity emitted Yul from converging beyond behavior-level parity.

Related broad roadmap issue: #1982.

Start with scripts/report_yul_identity_gap.py and the generated out/parity-target/morpho-midnight/report.json from the c3bed0e Verity pin to understand the reported helper drift. Review the codegen and lowering entry points that produce the Yul identity output, then define which solc-shaped helper behavior is feasible. Done means the configured gate reports a materially reduced or explicitly classified internal helper surface for the parity target.