[Java] Tool-as-lambda 4.2: Implement ToolDefinition from*/fromAsync* overloads

[edburns]

Overview

Implement Phase 4.2 of #1810: add typed ToolDefinition overloads for inline lambda-defined tools.

Before coding

• Do not start any implementation work until this issue is explicitly assigned to the coding agent.
• Base branch for this work: edburns/1810-java-tool-ergonomics-tool-as-lambda.
• Read this plan file on the branch before coding:
  1810-java-tool-ergonomics-tool-as-lambda-remove-before-merge/1810-ignorance-reduction-for-implementation-plan.md

Ordering rule (important)

This issue starts only after 4.1 is merged; all Phase 4 issues are completed in listed order.

Relevant Phase 3 resolutions to apply

• 3.1 API shape: implement v1 overload families and arity decisions from the plan.
• 3.2 ambiguity avoidance: separate sync/async by method families (from* vs fromAsync*) and use JDK functional interfaces.
• 3.4 behavior parity: support the same parameter-type surface as existing Java tool schema pipeline.
• 3.5 coercion policy: reuse existing ObjectMapper-based conversion behavior.
• 3.6 options flags: options are set via existing immutable fluent modifiers on ToolDefinition (overridesBuiltInTool, skipPermission, defer) rather than a new options object.
• 3.7 validation boundaries: fail fast with precise IllegalArgumentException messages.

Scope / deliverables

1. Update java/src/main/java/com/github/copilot/rpc/ToolDefinition.java with the resolved from* overloads.
2. Wire overloads to invocation adapter logic so sync/async and context-aware handlers behave correctly.
3. Ensure constructed definitions preserve existing runtime contract (String passthrough, void -> "Success", JSON serialization for non-String, async support).

Gating criteria

• Overloads compile cleanly and are unambiguous at common lambda call sites.
• Invocation paths are ready for unit tests in 4.4.

Constraints

• Keep this issue focused on overload implementation and wiring.
• No unrelated refactors.

Completion bookkeeping

When complete, update the checkbox for Phase 4.2 in:
1810-java-tool-ergonomics-tool-as-lambda-remove-before-merge/1810-ignorance-reduction-for-implementation-plan.md