Add isLocal flag to uriToLocalFile and use it

Expose an isLocal boolean from uriToLocalFile to indicate user-owned files vs temporary downloads/decodes, and update callers to avoid deleting or cleaning up user local files. Update OneBot file APIs to accept the isLocal hint (including createValidSendFileElement/createValidSendPicElement/createValidSendVideoElement) and adjust temp-file handling for videos: local files are copied into the NapCat temp dir with a random UUID filename to avoid polluting user directories, while temporary files get an added extension in-place. Also adjust deleteAfterSentFiles usage, image/video thumb handling, and numeric parsing fallbacks for element fileSize to be more robust. Minor imports (randomUUID) and related callsites were updated accordingly.