feat: add erc7201 builtin

[DaniPopes]

Closes #867.

This adds the solc 0.8.35 erc7201(string memory) builtin as a pure global builtin returning uint256. Constant evaluation and codegen use the ERC-7201 namespace slot formula, including the full-width subtraction before masking the low byte.

The new UI coverage lives under tests/ui/erc7201 and ports matching solc cases for accepted arguments, invalid calls, constant assignment, layout at, compile-time evaluation, and MIR lowering for literal, memory, calldata, and storage string inputs.

[codspeed-hq]

Merging this PR will not alter performance

✅ 76 untouched benchmarks

---

_{Comparing dani/erc7201-builtin (3716793) with main (d5b459f)}