Ufs serve fix - makes it work better on esp32cam (ai thinker style)

[btsimonh]

Description:

Related issue (if applicable): fixes #21473

This changes the rarely used UFSServe code enabled by #ifdef UFILESYS_STATIC_SERVING to be like the file download code.

For me, this makes the file serving much more reliable on slower devices like the ESP Chip Id 3667140 (ESP32-D0WDQ6 v1.0)

Prior to this change, I would see a random main loop hang on accessing files.

I have tested with >5000 file downloads on ESP32S3 and >1500 downloads on esp32cam (ai thinker style), and had better results. I don't think this is a complete fix, as I have had one device lose connection (unfortunately without serial) - but this could have been something else.

This PR also adds yield() in file list from the GUI. This is tested and does not cause a watchdog on a 1500 file folder. (the main thread is hung during this time - many seconds). I'm not sure if there can be a better solution whilst the webserver can handle a single client. One would be a re-write of the JS to poll for more files - but this may not help as even finding files in a large folder takes a lot of time. Having this many files in a folder on an IOT device seems unusual, so it may be better to document and live with it.

Checklist:

• [x] The pull request is done against the latest development branch
• [x] Only relevant files were touched
• [x] Only one feature/fix was added per PR and the code change compiles without warnings
• [ ] The code change is tested and works with Tasmota core ESP8266 V.2.7.6
• [x] The code change is tested and works with Tasmota core ESP32 V.3.0.0
• [x] I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass

[btsimonh]

@Jason2866 - pls comment on the use of yield in file listing.

[Jason2866]

yield does give the core time "doing needed" things and resets the WDT. So probably a good idea :-) What I do not like very much is the left debug code. Either you think it is needed so keep it active (maybe change to more debug) or remove it completely.

[s-hadinger]

Looks good to me. Ok to merge

[btsimonh]

@Jason2866 - point taken. none of it is active, as it's all hashed out.