feat: Yul bit-slicing engine, delegatecall forwarder, batch balance checker, G015 storage packer

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Summary

• [CORE] Build High-Performance Yul Bitmask & Array Slicing Engine #695 — contracts/utils/YulBitSlice.sol: pure-Yul library with extractBits(bytes calldata, bitOffset, bitLength) that reads arbitrary bit-length slices directly from calldata via calldataload, handling slices that straddle a 32-byte word boundary, without copying the buffer into memory. Also adds a byte-aligned sliceBytes convenience wrapper.
• [CORE] Implement Zero-Overhead Universal Delegatecall Forwarder in Yul #691 — contracts/proxy/YulProxyForwarder.sol: minimal fallback/receive forwarder that does calldatacopy → delegatecall(gas(), implementation, ...) → returndatacopy → return/revert, entirely in assembly, so proxied calls only pay for those four opcodes plus the delegatecall itself.
• [PERF] Build Assembly Multi-Token Balance Query Loop #690 — contracts/utils/BatchBalanceChecker.sol: batchBalances(tokens, accounts) builds the balanceOf(address) selector once, then loops over the token x account matrix with staticcall, writing results into a flat memory array. Reverting or non-contract targets resolve to 0 instead of aborting the whole batch.
• [CORE] Rule G015: Automated AST Storage Slot Re-Ordering Transformer #692 — gasguard-cli Rule G015: new transformers::storage_packer module that classifies state variable declarations (reusing the existing storage_model packing algorithm), then rewrites the contract source to group packable variables into shared 256-bit slots. Leading comments stay attached to their variable, and everything outside the declaration run (imports, structs, functions) is left byte-for-byte untouched. Wired up behind a new reorder-storage CLI command alongside the existing optimize-storage. Also added gasguard-cli/test/fixtures/storage_packing_transform.sol as a worked example (5 slots → 2 slots).

Assumptions / scope notes

• The G015 transform only reorders the contiguous run of simple state-variable declarations (no initializer, no function/struct/mapping-with-body noise) in the first contract/library body — it intentionally does not attempt a full AST rewrite of arbitrarily interleaved declarations, matching the lightweight text-based parsing style already used by commands::optimize_storage.
• gasguard-cli/Cargo.toml needed an explicit [workspace] table added — the crate wasn't previously buildable/testable at all (cargo test failed immediately with "current package believes it's in a workspace when it's not") because it isn't listed in the root Cargo.toml workspace members. This is a minimal, non-invasive fix so the new tests (and the crate generally) can actually run; it does not add gasguard-cli to the root workspace.
• test/*.test.ts files for the new Solidity contracts follow the exact structure of the existing test/utils/MappingResolver.test.ts and other test/**/*.test.ts files in this repo — note that these files use vitest imports and are not currently picked up by the npm test (jest) script, whose testRegex only matches *.spec.ts$. That's a pre-existing repo-wide condition affecting all test/**/*.test.ts files, not something introduced here.

Test plan

• forge build contracts/utils/YulBitSlice.sol contracts/proxy/YulProxyForwarder.sol contracts/utils/BatchBalanceChecker.sol — compiles cleanly (Solc 0.8.20)
• cd gasguard-cli && cargo test — all new transformers::storage_packer tests pass (7/7); 2 pre-existing failures in commands::optimize_storage reproduce identically on main and are unrelated to this change (out of scope)
• Maintainer review of the G015 reordering heuristic and Yul assembly safety comments

Closes #690
Closes #691
Closes #692
Closes #695

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