feat(codegen): emit solc-shaped ABI, allocation, arithmetic, and library Yul helpers

[Th0rgal]

Context

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

Current function-level drift has no hash mismatches, but still has 75 onlyInSolidity functions. The largest Solidity-only families are solc generated helpers:

• fun_*: 16 keys (fun_hasCredit, fun_isHealthy, fun_mulDivUp, fun_touchMarket, fun_updatePosition, etc.)
• update_storage_value*: 9 keys for packed/offest storage writes
• abi_decode_address*: 7 keys
• finalize_allocation*: 4 keys
• abi_decode_struct*: 3 keys
• checked arithmetic helpers: 9 total across add/sub/mul/div/mod families

Feature request

Add a Solidity-parity Yul helper emission mode for common solc helper families, so Verity-generated Yul can intentionally emit solc-shaped helper functions when targeting Yul identity against Solidity irOptimized output.

High-value helper families from the Midnight report:

• ABI encode/decode helpers for address, bool, bytes, dynamic arrays, and structs.
• Memory allocation helpers such as finalize_allocation and array_allocation_size_*.
• Checked arithmetic helpers matching solc 0.8 overflow semantics and helper names where feasible.
• Library/internal fun_* helper emission for Solidity-shaped functions used by Midnight.

Why this matters

These helpers are the largest Solidity-only part of the Midnight Yul identity manifest after the Verity-only internal helper drift. Closing them would substantially reduce the fail-closed manifest and make the Verity artifact structurally closer to solc output.

Related issues: #1982 (broad roadmap), #1993 (checked arithmetic), #2055 (dynamic calldata decoder refinement).