fix(execution): optimize tools.search performance and support multi-namespace search (#1935)

[Adityakk9031]

Summary

Resolves #1935 by resolving timeouts in tools.search when namespace is omitted or multiple slugs are searched in a single execution run.

Root Cause

1. searchTools performed an unbounded executor.tools.list() across all integrations on every invocation, triggering full workspace table scans and policy checks.
2. prepareField and scoreToolMatch re-normalized and re-tokenized query strings and large OpenAPI tool descriptions in a loop for every tool in the catalog.
3. tools.search lacked array/multi-namespace support, causing agents to batch independent searches and multiply runtime cost.

Solution

• Precompute query normalization/tokenization once outside the tool scoring loop.
• Use single-pass normalization and Set-based O(1) token lookups in prepareField.
• Directly scope executor.tools.list({ integration }) for exact namespace enumeration.
• Support namespace: string | string[] (array and comma-separated slug lists) in tools.search.

Verification

• bun run --cwd packages/core/execution test -- src/tool-invoker.test.ts (41 passed)
• bun run --cwd packages/hosts/mcp test (221 passed)
• bun run --cwd packages/core/execution typecheck
• bun run lint