Support Falcon PADDED format

[SWilson4]

Support the fixed-size PADDED format for Falcon signatures and update the existing Falcon code (which intends to implements the COMPRESSED format) to bring it in line with the spec. Reenable Falcon-1024 in weekly extended KAT tests, as it should now pass.

A couple of points to make review simpler:

• The only differences between the COMPRESSED and PADDED code should be contained in api.h and pqclean.c. It's probably worth looking at a side-by-side diff of these: for example, pqclean_falcon-512-padded_clean/pqclean.c vs pqclean_falcon-512_clean/pqclean.c.
• There are no NIST KATs available for the PADDED variant, so I generated my own from the Falcon reference implementation: see https://github.com/SWilson4/falcon-padded-KATs.
• The corresponding upstream PR is Support Falcon PADDED signature format PQClean/PQClean#530.

Fixes #1561 and #1608.

• Does this PR change the input/output behaviour of a cryptographic algorithm (i.e., does it change known answer test values)? (If so, a version bump will be required from x.y.z to x.(y+1).0.)
• Does this PR change the list of algorithms available -- either adding, removing, or renaming? Does this PR otherwise change an API? (If so, PRs in fully supported downstream projects dependent on these, i.e., oqs-provider and OQS-OpenSSH will also need to be ready for review and merge by the time this is merged.)

[SWilson4]

@Frauschi Can you please take a look at the Zephyr test failure? It looks like an out-of-storage error to me, and I'm unsure of the best way to resolve it. The same test fails on the current main, so it's not specific to this PR.

[SWilson4]

The oqs-provider release tests have passed on this branch and the appropriate tracker: https://github.com/open-quantum-safe/oqs-provider/actions/runs/8101766836/job/22142722419

[baentsch]

@Frauschi Can you please take a look at the Zephyr test failure? It looks like an out-of-storage error to me, and I'm unsure of the best way to resolve it. The same test fails on the current main, so it's not specific to this PR.

Indeed, what does "No space left on device" mean in this context? Also FYI, @Frauschi we're aiming of doing a liboqs release containing this PR early next week so resolving this quickly would be very helpful & appreciated.

[Frauschi]

@Frauschi Can you please take a look at the Zephyr test failure? It looks like an out-of-storage error to me, and I'm unsure of the best way to resolve it. The same test fails on the current main, so it's not specific to this PR.

Indeed, what does "No space left on device" mean in this context? Also FYI, @Frauschi we're aiming of doing a liboqs release containing this PR early next week so resolving this quickly would be very helpful & appreciated.

I just created PR #1714 that should fix the failing Zephyr CI tests. The problem was the Zephyr installation that has been created within the test environment. A default Zephyr installation is several GBs in size, apparently overfilling the disk space of the Github runner. Hence, the "No space left on device".

[baentsch]

Thanks for all this work, @SWilson4 !

[baentsch]

Just as reminder: This needs changing before final merge.