scalar: refactor: use secp256k1_{read,write}_be32 helpers #1339

1. 
   theStack commented at 6:45 pm on June 10, 2023: contributor

   This refactoring PR takes use of the secp256k1_{read,write}_be32 helpers (introduced in PR #1093, commit 8d89b9e6e562000cdb91a70a85fae5e4817cec8a) in the scalar <-> byte array conversion functions, for both the 8x32 and 4x64 implementations. (An alternative for the latter would be to introduce special helpers for reading/writing uint64_t in big endian secp256k1_{read,write}_be64).

   Verified via objdump -D libsecp256k1.a that secp256k1_scalar_set_b32 for 4x64 compiles to the same code on master and the PR (secp256k1_scalar_get_b32 is apparently always inlined) on amd64 with clang 13.0.0.

2. scalar: use `secp256k1_{read,write}_be32` helpers (8x32 impl.) 52b84238de
3. scalar: use `secp256k1_{read,write}_be32` helpers (4x64 impl.)

   An alternative would be to introduce special helpers for reading/writing
   uint64_t in big endian `secp256k1_{read,write}_be64`.

   887183e7de
4. real-or-random approved
5. 
   real-or-random commented at 10:47 am on June 11, 2023: contributor

   utACK 52b84238de27889f2517c845757bf5c2c65ed1d6
6. real-or-random added the label refactor on Jun 11, 2023
7. 
   sipa commented at 2:53 pm on June 12, 2023: contributor

   utACK 887183e7de4d1941792d78471a3adb004fd4ec8e

   As a follow-up, it may make sense to consider adding secp256k1_{read,write}_be64 functions too.

8. real-or-random merged this on Jun 12, 2023
9. real-or-random closed this on Jun 12, 2023

   ---

10. theStack deleted the branch on Jun 12, 2023
11. theStack cross-referenced this on Jun 17, 2023 from issue scalar: introduce and use `secp256k1_{read,write}_be64` helpers by theStack
12. real-or-random referenced this in commit 45c5ca7675 on Jun 18, 2023
13. sipa referenced this in commit 901336eee7 on Jun 21, 2023
14. vmta referenced this in commit 8f03457eed on Jul 1, 2023
15. hebasto referenced this in commit 270d2b37b8 on Jul 21, 2023
16. jonasnick cross-referenced this on Jul 26, 2023 from issue Upstream PRs 1314, 1317, 1318, 1316, 1327, 1310, 1328, 1333, 1330, 1334, 1337, 1341, 1339, 1350, 1349, 1338, 1129, 1347, 1336, 1295, 1354, 1355, 1356 by jonasnick

Contributors
theStack real-or-random sipa

Labels
refactor/smell