Solidity version pinning: generate pinned() wrappers in the .cdm/solidity imports

Problem

Since #76, Solidity consumers get the stable per-name proxy address baked into their generated imports (.cdm/solidity/<scope>/<pkg>.sol), but calls through the typed ref() interface are plain calldata — the proxy routes them to the latest implementation. The version pinned at cdm install time affects only the generated interface's shape, not execution.

No toolchain blocker — this is pure codegen

Solidity's low-level .call/.staticcall accept arbitrary bytes, and the import files are generated by solidity-imports.ts (fully owned here). The generator can bake the CDM wire prefix as constants and emit one pinned wrapper per ABI method:

// generated — users never write this
bytes4  private constant CDM_MAGIC = 0xa2264d53;             // keccak256("cdm.proxy.call.v1")[..4]
uint128 private constant CDM_KEY   = <major<<64|minor<<32|patch>; // pinned at install time

function increment() internal {
    (bool ok, bytes memory ret) = ADDRESS.call(
        abi.encodePacked(CDM_MAGIC, CDM_KEY, abi.encodeCall(IExampleCounter.increment, ()))
    );
    if (!ok) _bubble(ret); // revert with the proxy/impl's exact revert data
}

User surface becomes a choice of two one-liners:

ExampleCounter.ref().increment();      // follow latest (today's behavior)
ExampleCounter.pinned().increment();   // execute exactly the installed version

Details

• Views/pure → staticcall; returns abi.decoded in the generated wrapper.
• Reverts bubble the raw returndata so proxy errors (UnsupportedVersion(uint128,uint128), ContractFrozen(), …) surface with their real selectors.
• The pinned() shape (library of free functions vs a struct-wrapped handle mirroring ref()) is the main design choice — whatever reads best next to the existing ref()/cdm() surface.
• Constants derive from the same pinned version the generator already receives; cdm i regenerates on version change as it does today.

References

• #76 — wire format and on-chain routing (e2e-proven in proxy.e2e.test.ts); src/lib/contracts/src/solidity-imports.ts — the generator this lands in. TypeScript and Rust pinning are tracked separately.

Start in src/lib/contracts/src/solidity-imports.ts and compare the existing ref()/cdm() generated surface with the pinned() design options described in the issue. Use the wire format and routing behavior from #76 and proxy.e2e.test.ts as references. Done means generated imports expose pinned wrappers that route to the installed version, decode view/pure returns, use staticcall where appropriate, and preserve raw revert data.