serve dlna: log unescaped paths - fixes #7370 - #9950

What does this change do?

serve dlna logged each request against request.URL, which prints escaped. Non-ASCII file names showed up as runs of %XX:

INFO  : /r/%D0%91%D0%B0%D1%80%D0%B4%D1%8B/%D0%9F%D0%B0%D0%B2%D0%B5%D0%BB%D0%B5%D1%86%D0%BA%D0%B8%D0%B9%20%D0%B2%D0%BE%D0%BA%D0%B7%D0%B0%D0%BB.mp3: 127.0.0.1:54940 GET 200

It now logs request.URL.Path, the unescaped path:

INFO  : /r/Барды/Павелецкий вокзал.mp3: 127.0.0.1:36062 GET 200

This is what the other serve loggers already use: webdav, s3, the lib/http auth logging, and dlna's own panic log.

There is no flag, as agreed in the issue. As a result:

• the query string is no longer shown;
• an escaped / (%2F) shows as /.

Both are the same as in the other serve commands.

Testing

• TestLoggingUnescapedPath sends a request with an escaped Cyrillic path containing a space through logging(), and checks that the log line has the unescaped path. It fails on master.
• The test captures the log with bilib.CaptureOutput, as the fs/sync and fs/operations tests do. It uses a 404 so the line is logged at ERROR, which means it doesn't have to change ci.LogLevel. Changing that would race under -race with the SSDP goroutines of the dlna server that TestInit leaves running.
• Manual check: I ran rclone serve dlna on a directory holding Барды/Павелецкий вокзал.mp3 and fetched the file with curl. The two log lines above are from master and from this branch.
• These pass: go build ./..., make quicktest, go test -race ./cmd/serve/dlna/, go vet and golangci-lint run ./cmd/serve/dlna/....

Linked issue

Fixes #7370

Checklist

• This change is trivial OR it has been discussed and agreed in the linked issue.
• I have read the contribution guidelines.
• (If I used AI tools to help write this code) I have read and understood the AI-assisted contributions guidance, and I have tested and take ownership of this change myself.
• I have added tests for all changes in this PR if appropriate.
• I have added documentation for the changes if appropriate. (No doc change needed: log output only.)
• All commit messages are in house style.
• (Backend changes only) test_all passes for this backend. n/a, not a backend change.
• This Pull Request is ready for review.