fix: isolate signatures array across QueryBuilder instances - #11

Problem

QueryBuilder.from() stores signatures in a shared mutable array. Each withSignatures() call pushes to the same array, so signatures accumulate across all derived instances:

const qb = QueryBuilder.from(is)

const a = qb.withSignatures(['event Transfer(address indexed from, address indexed to, uint256 tokens)'])
// signatures = ['event Transfer(... uint256 tokens)']

const b = qb.withSignatures(['event Transfer(address indexed from, address indexed to, uint256 amount)'])
// signatures = ['event Transfer(... uint256 tokens)', 'event Transfer(... uint256 amount)']
// ^^^ instance `a` is now also contaminated with the second signature

This breaks queries for events that share the same event selector but differ in parameter names (e.g. ERC-20 Transfer with uint256 tokens vs uint256 amount). The Driver receives the accumulated list, so the wrong signature may be used for column name resolution, leading to errors like column "amount" does not exist.

Fix

Create an immutable snapshot of the signatures array for each inner() call. Each QueryBuilder instance now gets its own isolated copy of signatures:

- const signatures: string[] = []
+ let signatures: string[] = []

  function inner(o = {}) {
    cursor ??= o.cursor
-   signatures.push(...(o.signatures ?? []))
+   signatures = [...signatures, ...(o.signatures ?? [])]
+
+   const sigs = [...signatures]

    const kysely = new Kysely({
      dialect: {
-       createDriver: () => new Driver({ ...options, cursor, signatures }),
+       createDriver: () => new Driver({ ...options, cursor, signatures: sigs }),
        // ...
      },
    })

Reproduction

1. Create a QueryBuilder via from()
2. Call withSignatures() with signature A, use the returned builder for a query
3. Call withSignatures() with signature B (same event name, different param names)
4. The query from step 2 now has both signatures — the backend may resolve columns using the wrong one