feat: add fetchCanisterLogs method to PocketIc

[yasumorishima]

Summary

Adds a fetchCanisterLogs() method to the PocketIc class, implementing the fetch_canister_logs management canister query call.

This allows users to programmatically retrieve canister log records, which is especially useful for debugging traps in timers and heartbeats that are otherwise invisible.

Closes #68

Changes

• management-canister.ts: Add Candid IDL types, TypeScript interfaces, and encode/decode functions for fetch_canister_logs
• pocket-ic-types.ts: Add FetchCanisterLogsOptions and CanisterLogRecord public types
• pocket-ic.ts: Add fetchCanisterLogs() method that makes a query call to the management canister with effectivePrincipal set to the target canister
• main.mo: Add print_log method to test canister for testing
• fetchCanisterLogs.spec.ts: Add 2 test cases (fetch logs after Debug.print + empty logs for fresh canister)

Implementation notes

• Follows the same pattern as the Rust library implementation
• Uses effectivePrincipal: { canisterId } as required by the IC spec for management canister queries
• The caller must be a controller of the target canister (anonymous principal is rejected)
• Maps timestamp_nanos to timestampNanos in the public type to follow the project's camelCase convention

Test plan

• pnpm run build passes
• pnpm run test:pic — all 13 tests pass (11 existing + 2 new)
• pnpm run format:check passes
• e2e tests pass (Node.js + Bun, ubuntu + macos)