Add preprocessor option for asynchronous erase support

[LithosphereRocketry]

Pull request details

• Please check if the PR fulfills these requirements

• The commit message/s explain/s all the changes clearly
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• Bug fix
• Added feature
• Documentation update
• Other - Please explain here:

• What is the current behavior? (You can also link to an open issue here)

When erasing a page, the current library busy-waits until the erase is confirmed completed.

• What is the new behavior? (if this is a feature change)

When ERASE_ASYNC is defined, the wait for the chip to be ready is removed. This should not impact reliability in most cases, as all functions wait for ready at the start of execution as well.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

It removes a check for ready at the beginning of suspendProg(); this should break almost nothing, as suspendProg() has no purpose without this PR, but it in theory could introduce some strange behavior e.g. if you try to suspend during a whole-chip erase.

• Other information:

I couldn't for the life of me get Sphinx working on my system, so the HTML docs aren't built, but the source files are updated.

Currently only tested on STM32 with W25Q128 as that's the hardware I have on hand - would appreciate testing on other configurations.

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