Previously, all templates were named with the .html extension, which caused problems for editors to recognize the Jinja2 syntax used in them. In this commit, all templates have been renamed to use the .jinja2 extension to better reflect their use of Jinja2 and to improve editor recognition.
Update current player showcase after updating character list.
Use asynchronous locks to make file read/write thread-safe.
Update `EnkaNetworkCache`.
---------
Co-authored-by: 洛水居室 <luoshuijs@outlook.com>