Fix cache eviction order, redundant matchesQuery recursion, and sync/async misuse

[Copilot]

Several correctness and performance issues found during architectural review of the core KV primitives.

Cache eviction was backwards (+ falsy-zero bug)

KVLedgerCache.evictOldestEntries() used pop() — removing the newest entry — instead of shift() to remove the oldest. The documented intent is FIFO eviction; the implementation was LIFO, so freshly-written entries were discarded while stale ones accumulated.

Separately, if (oldestOffset) silently skipped eviction for any entry at offset 0 (falsy), leaking memory.

// Before: evicts newest, skips offset 0
const oldestOffset = this.cacheEntries.pop() as number;
if (oldestOffset) { ... }

// After: evicts oldest, handles offset 0
const oldestOffset = this.cacheEntries.shift();
if (oldestOffset !== undefined) { ... }

matchesQuery() did redundant O(n²) recursive work

Inside the for loop, at every step i, the code created a new KVKeyInstance, sliced both key and query arrays, and re-ran matchesQuery on the tail — work the outer loop was already doing in subsequent iterations. Removed entirely; behavior is unchanged.

KVIndex.get() called key.get() on every recursion

key.get()[keyIndex] inside the inner recurse function re-invoked the getter on every call. Cached to const keyParts = key.get() once before entering recursion.

Unnecessary await on sync methods in kv.ts

transaction.create() and transaction.toUint8Array() are synchronous but were called with await, misleading readers about the async nature of the surrounding code.

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