feat(java): Add ToolDefinition.fromObject() and fromClass() registration API

[Copilot]

Adds the runtime registration API that loads processor-generated $$CopilotToolMeta companion classes and returns List<ToolDefinition> with fully working handlers. This is task 4.4 in the tool ergonomics epic.

Changes

• ToolDefinition.java — two new @CopilotExperimental static methods:

  • fromObject(Object) — for instance methods annotated with @CopilotTool
  • fromClass(Class<?>) — for static @CopilotTool methods (passes null instance)
  • Private loadDefinitions() uses Class.forName with the target classloader, setAccessible(true), and passes a configured ObjectMapper
  • ConfiguredMapperHolder — lazy-init mapper matching JsonRpcClient.createObjectMapper() (JavaTimeModule, lenient unknown-props, ISO dates, NON_NULL)
  • Throws IllegalStateException with actionable message if $$CopilotToolMeta not found — no reflection fallback

• ToolDefinitionFromObjectTest.java — 13 gating tests with hand-written meta fixtures covering: tool discovery, schema validation, handler invocation (String/void/CompletableFuture), argument coercion (primitives + enum), default values, missing-class error, java.time deserialization via ObjectMapper contract, override flag, and ToolDefer.NONE → null JSON omission

Usage

class MyTools {
    @CopilotTool("Get weather for a city")
    public String getWeather(@Param("City name") String city) {
        return fetchWeather(city);
    }
}

// At runtime — processor must have run at compile time
List<ToolDefinition> tools = ToolDefinition.fromObject(new MyTools());
session.setTools(tools);