Migrate to `ff` revision with square root backports

[codecov-commenter]

Codecov Report

Base: 67.32% // Head: 68.52% // Increases project coverage by +1.19% :tada:

Coverage data is based on head (1c21a89) compared to base (f8ba48d). Patch coverage: 63.63% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #52 +/- ## ========================================== + Coverage 67.32% 68.52% +1.19% ========================================== Files 11 11 Lines 1261 1204 -57 ========================================== - Hits 849 825 -24 + Misses 412 379 -33 ``` | [Impacted Files](https://codecov.io/gh/zcash/pasta_curves/pull/52?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zcash) | Coverage Δ | | |---|---|---| | [src/fields/fp.rs](https://codecov.io/gh/zcash/pasta_curves/pull/52/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zcash#diff-c3JjL2ZpZWxkcy9mcC5ycw==) | `79.28% <50.00%> (-1.71%)` | :arrow_down: | | [src/fields/fq.rs](https://codecov.io/gh/zcash/pasta_curves/pull/52/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zcash#diff-c3JjL2ZpZWxkcy9mcS5ycw==) | `78.57% <50.00%> (-1.72%)` | :arrow_down: | | [src/arithmetic/fields.rs](https://codecov.io/gh/zcash/pasta_curves/pull/52/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zcash#diff-c3JjL2FyaXRobWV0aWMvZmllbGRzLnJz) | `93.90% <100.00%> (+29.01%)` | :arrow_up: | | [src/curves.rs](https://codecov.io/gh/zcash/pasta_curves/pull/52/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zcash#diff-c3JjL2N1cnZlcy5ycw==) | `54.38% <100.00%> (ø)` | | | [src/hashtocurve.rs](https://codecov.io/gh/zcash/pasta_curves/pull/52/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zcash#diff-c3JjL2hhc2h0b2N1cnZlLnJz) | `70.14% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zcash). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zcash)

:umbrella: View full report at Codecov.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.

[str4d]

Force-pushed to fix lint.

[str4d]

Force-pushed to fix the zkcrypto/ff revision after the PR there was force-pushed.

[str4d]

Rebased on main to fix merge conflict.