fix(ai): resume input-streaming tool calls

[iroiro147]

Summary

• Seed resumed UI message stream state from existing input-streaming tool parts.
• Continue tool-input-delta chunks for both static and dynamic tool calls after hydration.
• Add regression coverage for resuming in-progress static and dynamic tool inputs.

Closes #14027.

Tests

• pnpm -C packages/ai exec vitest --config vitest.node.config.js --run src/ui/process-ui-message-stream.test.ts
• pnpm -C packages/ai exec vitest --config vitest.edge.config.js --run src/ui/process-ui-message-stream.test.ts
• pnpm -C packages/ai type-check
• pnpm --filter ai build
• pnpm exec oxfmt --check packages/ai/src/ui/process-ui-message-stream.ts packages/ai/src/ui/process-ui-message-stream.test.ts .changeset/chat-resume-tool-input.md
• pnpm exec oxlint packages/ai/src/ui/process-ui-message-stream.ts packages/ai/src/ui/process-ui-message-stream.test.ts --deny-warnings
• pnpm changeset status --since origin/main
• git diff --check

[vercel]

The resume input-streaming tool calls feature never works in a real flow because rawInput is never persisted on input-streaming tool parts during the initial stream (and would be stripped by validateUIMessages even if present), so the resumed partial JSON always starts from an empty string.