Allow specifying known flash size during OTA to make erasing faster

[Calsign]

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Pull Request Details 📖

Description

The OTA process requires first erasing data in the flash partition and then writing the new image. By default the entire image is erased, even though we only need to erase enough space to fit the image. For esp32s with large flash sizes and relatively small images, the erasing can dominate total OTA time.

This PR adds an initiate_update_with_known_size variant to allow passing through the size parameter to the underlying ESP IDF library rather than the default OTA_SIZE_UNKNOWN.

Testing

I tested by using by specifying the size when performing an OTA. For me, this sped up the erase portion of OTA by 3x. (esp32s3 with 32M flash, two 8M OTA partitions, actual image considerably smaller than that)