feat: implement thread-safe synchronous blocking client wrapper

[stenalpjolly]

Summary

This pull request implements the thread-safe synchronous blocking client wrapper (McpToolboxSyncClient and HttpMcpToolboxSyncClient) for the Java SDK, providing an idiomatic blocking interface over the underlying asynchronous (CompletableFuture-based) McpToolboxClient.

Dependencies:

• Depends on PR 1 (decoupled checked/unchecked exception hierarchy: McpToolboxException, McpProtocolException, McpTransportException, ToolExecutionException, plus connect/request timeout and custom logger builder options).
• Depends on PR 2 (buildSync() interface and implementation on McpToolboxClient / McpToolboxClientBuilder, plus transport constructors supporting timeout and logging configurations).

Expectation & Implementation

Expectations

• Provide an idiomatic, pure synchronous blocking experience without requiring callers to manually call .join() or handle CompletionException / CancellationException.
• Ensure all checked and concurrent execution exceptions are cleanly unwrapped into the unchecked McpToolboxException hierarchy.
• Maintain full thread safety across synchronous tool invocations (Tool.executeSync).

Implementation Details

• McpToolboxSyncClient interface: Defines synchronous counterparts for tool discovery (listTools, loadToolset), tool loading (loadTool), and tool execution (invokeTool).
• HttpMcpToolboxSyncClient class: Implements McpToolboxSyncClient by delegating to an underlying McpToolboxClient and blocking via .join(). Unwraps CompletionException and CancellationException cleanly into appropriate McpToolboxException instances or IllegalArgumentException.
• Builder Integration: Added buildSync() to McpToolboxClient.Builder and McpToolboxClientBuilder to construct HttpMcpToolboxSyncClient directly.
• Tool.executeSync(): Added synchronous execution wrapper directly on Tool instances.
• Exception Hierarchy: Introduced McpToolboxException (base unchecked exception), McpProtocolException, McpTransportException, and ToolExecutionException (from PR 1 dependency foundation).
• Transport Configuration: Extended BaseMcpTransport and versioned HTTP transports with connectTimeout, requestTimeout, and custom Logger support (activeLogger).
• Documentation: Updated README.md to highlight both async-first and sync-first usage patterns.

Test cases

• McpToolboxSyncClientTest: Verified constructor validation (null delegate checks).
• McpToolboxSyncClientTest: Verified builder configuration, buildSync(), connect/request timeouts, and custom logger propagation.
• McpToolboxSyncClientTest: Verified delegation of all synchronous methods (listTools, loadToolset, loadTool, invokeTool).
• McpToolboxSyncClientTest: Verified comprehensive exception unwrapping (McpToolboxException, IllegalArgumentException, generic Exception, and null cause).
• McpToolboxSyncClientTest: Verified Tool.executeSync() exception handling and deep-copying support for complex List parameter default values.
• McpToolboxClientBuilderTest: Verified McpTransportException constructors and status codes.
• HttpMcpTransportTest: Verified HTTP request timeout configuration during tool invocation.

Acceptance criteria

• All 140 unit tests pass with BUILD SUCCESS.
• 100.00% line coverage achieved on HttpMcpToolboxSyncClient.java and McpToolboxSyncClient.java.
• All code formatted strictly using google-java-format under JDK 22+.
• Full thread-safe synchronous wrapper implementation cleanly decoupled from async internals.

Breaking changes

• None. This is an additive feature layer over the existing asynchronous client.

TAG=agy
CONV=c9cedc7f-5a6a-4d32-bf40-6e0ea2d21364