Extract shared validateLoadOptions helper

[corasan]

Summary

• Add a generic validateLoadOptions<T> helper in package/src/runtime.ts that guards on undefined and wraps onProgress with createSafeCallback.
• Collapse validateSTTLoadOptions, validateTTSLoadOptions, and validateEmbeddingsLoadOptions into one-line delegations to the helper.
• Route validateLLMLoadOptions through the helper, layering the existing tool-definition validation on top.
• Public API (signatures and return types) unchanged — no caller updates needed.

Test plan

• bun typescript passes
• bun test package/src/runtime.test.ts — 6 pass, 0 fail