feat(spi_nand_flash): add diagnostics application for NAND flash

[RathiSonika]

Change description

Added a diagnostics application for NAND flash to facilitate debugging and performance analysis.

[pacucha42]

Please, consider adding ESP_ERROR_CHECK wherever applicable. I didn't comment all single cases, however, we should provide clean-code example.

Beside of such minor points, all LGTM. Thanks

[igrr]

I think nand_read_write_sectors_tp isn't a great "API" now because it returns information by printing it to console. This means that it can only be used in a test/diagnostic application.

If we keep the function as is, I would suggest:

• Move the function definition to the new diagnostics example
• Remove benchmarking part of the test_app — this is now covered by testing the example.

If you would prefer to keep this as an API, I would suggest some changes:

• Combine most of function arguments into a structure. This way, if you need to add yet another argument or a benchmarking option, that won't be a breaking change.
• Instead of printing the results using ESP_LOG, fill in another "result" structure, return the structure to the caller using an output pointer, and let the caller print the results.

[RathiSonika]

Thank you for the review @igrr. I had considered this point earlier, but I’m not sure how the throughput would be used from the user’s perspective. This API is primarily designed for testing throughput, similar to how the iperf command works—where you provide arguments, and it prints the throughput. That was the idea behind creating this API. Of course, I can update it, but is it really necessary to return the time intervals required for reading and writing sectors?

[igrr]

Would it then be enough to define this benchmarking function within the diagnostics application/example? This way you aren't committing it any specific API — you are free to change the example at any time without making it a breaking change. And as you said, it's not clear how the throughput will be used from users' perspective. My guess that having a benchmarking application is enough and the users won't need to integrate this into their own apps.

[RathiSonika]

Yes, I’ll move this function to the diagnostics application as it’s a better option.

[igrr]

LGTM, just one nitpick.

[igrr]

Is it okay that the example depends on a private API?