fix: nest types under import/require in exports maps

[OsamaAnsar]

Fixes #182.

The bug

TypeScript's Node16/NodeNext resolver matches exports conditions by JSON key order against the currently-active condition set. Both @libsql/client and @libsql/core had types as a sibling key listed before import/require:

"./api": {
    "types": "./lib-esm/api.d.ts",
    "import": "./lib-esm/api.js",
    "require": "./lib-cjs/api.js"
}

Since types itself is always one of the active conditions (require, types, node or import, types, node), and it's the first matching key in the object, TypeScript picks it regardless of whether resolution is actually happening in CJS or ESM mode. So a CJS consumer's require resolution still lands on the ESM .d.ts, which then recursively resolves its own imports in ESM mode — producing exactly the TS1479 error from #182 ("this file is CommonJS ... but the referenced file is an ECMAScript module").

This affects @libsql/core too, which matters because @libsql/client's own entry point imports from it — fixing only the client package wasn't enough to fully resolve the repro.

The fix

• Nest types inside each import/require block instead of as a shared sibling, in both packages' exports maps (preserving every existing conditional target — workerd/deno/edge-light/etc. mappings are unchanged, just relocated).
• Flip declaration: false → true in both packages' tsconfig.build-cjs.json, since the new require.types entries point at lib-cjs/*.d.ts, which didn't previously exist.

Verification

Reproduced the issue exactly as described: a Node16-resolution CJS+TS consumer importing @libsql/client fails tsc --noEmit with TS1479 on current main, and passes cleanly after this fix. Checked a parallel ESM consumer too, to confirm no regression on that side (still resolves and typechecks correctly).

Ran the full jest suite before and after: identical result both times, 183 passing / 14 failing (all 14 are a pre-existing, unrelated Windows-specific EPERM issue in the test harness's temp-directory cleanup — reproduced identically on unmodified main, confirmed via git stash).