Add unchecked serialization/deserialization

[Pratyush]

Add unchecked serialization and deserialization, for the case when one knows that the serialized output will be stored in a trusted location (for example: serialized and deserialized by the same machine).

cc @ChaitanyaKonda @iAmMichaelConnor, this might solve your use case in a cleaner way.

cc also @kobigurk @paberr

[paberr]

I agree this is probably the cleaner way to do it. 👍
One remark though: The _unchecked variants are now incompatible with the _uncompressed methods for serialization/deserialization. The _unchecked implementations write the infinity bit explicitly into its own byte, while the _uncompressed code encodes it into the non-used bits.

Did you choose to use an explicit bool for performance reasons?
If yes, I think adding a note to the documentation would be good, indicating this difference.

[Pratyush]

Did you choose to use an explicit bool for performance reasons?

I did omit the flag handling for affine structs for performance reasons, but I should check that it actually makes a difference by benchmarking.

[kobigurk]

This is very useful! I actually might need something like this soon.
That said, I'm highly in favor of making it compatible with the normal decompression. @Pratyush do you think you're going to decide by benchmarking?

[Pratyush]

@kobigurk @paberr I think I'll just make it compatible with normal decompression, because I suspect most of the overhead is due to subgroup checks, and not due to bit manipulation. (I'm writing benchmarks right now to verify this)

[Pratyush]

I suspect most of the overhead is due to subgroup checks, and not due to bit manipulation.

Indeed, most of the overhead is due to the prime-group check.