* Refactor MountedProvider into FastMCPProvider + TransformingProvider
Split the monolithic MountedProvider into two focused components:
- FastMCPProvider: wraps a FastMCP server as a provider
- TransformingProvider: applies namespace/rename transformations to any provider
Add with_transforms() method to Provider base class for fluent API.
Rename mount() prefix parameter to namespace (deprecate prefix).
* Reuse compiled URI_PATTERN in deprecated import_server
