test(shared): add fast-check property tests

[kellenff]

Summary

• add fast-check as a development dependency
• add property-based coverage for request IDs and JSON-RPC schemas
• verify encode/decode round trips across generated messages and envelopes

Test plan

• pnpm run test — 81 tests passed
• pnpm run build — passed

Notes

• Build retains the existing direct eval warning in the client example.