Support for uppercase letters at the log level

Previously, fastmcp commands using uppercase log levels would fail to execute.

This update adds support for uppercase letters in log level
specifications.

e.g.
fastmcp run --transport streamable-http --host 0.0.0.0 -p 8000 --log-level DEBUG examples/echo.py

src/fastmcp/server/server.py

@@ -802,7 +802,7 @@ class FastMCP(Generic[LifespanResultT]):
         """
         host = host or self.settings.host
         port = port or self.settings.port
-        default_log_level_to_use = log_level or self.settings.log_level.lower()
+        default_log_level_to_use = (log_level or self.settings.log_level).lower()
 
         app = self.http_app(path=path, transport=transport, middleware=middleware)