[Server] Implement discovery caching for improved performance (#39)

* feat: implement discovery caching with state-based approach

- Add DiscoveryState class to encapsulate discovered MCP capabilities
- Add exportDiscoveryState and importDiscoveryState methods to Registry
- Modify Discoverer to return DiscoveryState instead of void
- Create CachedDiscoverer decorator for caching discovery results
- Add importDiscoveryState method to ReferenceRegistryInterface
- Update ServerBuilder to use caching with withCache() method
- Update tests to work with new state-based approach
- Add example demonstrating cached discovery functionality
- Add PSR-16 SimpleCache and Symfony Cache dependencies

* docs: add comprehensive discovery caching documentation

- Add detailed documentation explaining discovery caching architecture
- Include usage examples for different cache implementations
- Document performance benefits and best practices
- Add troubleshooting guide and migration instructions
- Include complete API reference for all caching components
- Fix PHPStan issues by regenerating baseline
- Apply PHP CS Fixer formatting to all new files

* refactor: address reviewer feedback and clean up discovery caching

- Make DiscoveryState class final
- Cache DiscoveryState objects directly instead of arrays (no serialization needed)
- Rename exportDiscoveryState/importDiscoveryState to getDiscoveryState/setDiscoveryState
- Add getDiscoveryState method to ReferenceRegistryInterface
- Remove TTL parameter from CachedDiscoverer (no expiration by default)
- Remove unused methods from DiscoveryState (toArray, fromArray, merge)
- Simplify ServerBuilder to handle decoration internally
- Make Discoverer.applyDiscoveryState() internal (no longer public API)
- Simplify documentation to focus on user perspective
- Remove unnecessary development comments
- Update all tests to work with new architecture
- All tests pass, PHPStan clean, code formatting applied

* refactor: clean up comments and formatting in server.php example

* refactor: improve code formatting and consistency in discovery classes and example server

* Fix method names in cached discovery example

- Change withServerInfo() to setServerInfo()
- Change withDiscovery() to setDiscovery()
- Change withLogger() to setLogger()
- Fixes PHPStan static analysis errors

* refactor: update method names in ServerBuilder for consistency

- Change withCache() to setCache() in ServerBuilder
- Update example and documentation to reflect method name changes
- Ensure consistency across caching implementation in examples and documentation

* refactor: reorganize examples and fix PHPStan baseline

- Move cached discovery example from examples/10 to examples/09
- Update composer.json autoload-dev namespace mapping
- Fix PHPStan baseline by removing invalid entries for non-existent files
- Update server.php to follow proper example pattern with logging and lifecycle

* fix: correct formatting in server.php

src/Capability/Registry/ReferenceRegistryInterface.php

@@ -11,6 +11,7 @@
 
 namespace Mcp\Capability\Registry;
 
+use Mcp\Capability\Discovery\DiscoveryState;
 use Mcp\Schema\Prompt;
 use Mcp\Schema\Resource;
 use Mcp\Schema\ResourceTemplate;
@@ -76,4 +77,15 @@ interface ReferenceRegistryInterface
      * Clear discovered elements from registry.
      */
     public function clear(): void;
+
+    /**
+     * Get the current discovery state (only discovered elements, not manual ones).
+     */
+    public function getDiscoveryState(): DiscoveryState;
+
+    /**
+     * Set discovery state, replacing all discovered elements.
+     * Manual elements are preserved.
+     */
+    public function setDiscoveryState(DiscoveryState $state): void;
 }