Bump rain-lib-memkv to 0.2.0: fingerprint the stateKV contents, not the handle word #585

Problem

rainlang pins rain-lib-memkv 0.1.5. rain.lib.memkv 0.2.0 (rainlanguage/rain.lib.memkv#166, closes rainlanguage/rain.lib.memkv#13) changes what a MemoryKV handle is. It is now the address of a 16-word header in memory instead of a packed word of 16-bit head pointers and a count. That removes the 64 KiB ceiling. A store can now grow past 0xFFFF instead of reverting MemoryKVOverflow. Function signatures, MEMORY_KV_EMPTY and the export pair order are unchanged. Two behaviours change:

• Copies of a non-empty handle are one store: inserts and updates show through every copy, and only the empty handle branches.
• After the first insert the handle word stops changing, so anything that hashes or compares the handle no longer sees inserts.

test/lib/state/LibInterpreterStateFingerprint.sol hashes abi.encode(state), which includes the stateKV handle word. On 0.2.0 an insert into a non-empty stateKV leaves the fingerprint unchanged. Updates were already invisible to it on 0.1.5.

Evidence (from the #166 adversarial review)

• rainlang main 5874169 with 0.2.0's LibMemoryKV.sol swapped into the 0.1.5 dependency path gives the same per-test pass/fail set as 0.1.5: 1492 pass, and the same 6 RPC-dependent constructor failures. No rainlang source copies, branches or restores a handle. Every use goes through state.stateKV and is assigned back: LibOpSet, the LibOpGet miss cache, the BaseRainlangInterpreter.eval4 overlay, the LibEval export, and the init in LibInterpreterStateDataContract.
• A probe built on the real LibOpSet.run and the real fingerprint helper passes on 0.1.5 and fails on 0.2.0 at "fingerprint must move on an insert into a non-empty stateKV". No existing rainlang test observes this, because every opReferenceCheck starts from an empty stateKV.
• Every rainlang test with a fixed gas figure that changed got cheaper; none got more expensive. Rainterpreter deploy gas fell by 107375.

Proposed fix

1. Bump rain-lib-memkv to 0.2.0 in foundry.toml and soldeer.lock, and rewrite the versioned import prefix rain-lib-memkv-0.1.5/ to the new one.
2. LibInterpreterStateFingerprint: hash the store's contents, for example stateKV.toBytes32Array(), instead of the handle word, so an insert into a non-empty store moves the fingerprint.
3. Update the gas figures that moved.
4. The Rainterpreter runtime bytecode changes, so the release needs a new deploy through rainlang.deploy. raindex, rain.erc4626.words, rain.flare, rain.merkle and rain.pyth pin rain-lib-memkv next to rainlang, and bump both together.