`rustfmt`: Run on `util/*` (2/2)

[tnull]

This is PR 2/2, based on #3324.

The diff is a bit larger for this one, but AFAICT the changes look mostly reasonable (besides the oddity commented below).

FWIW, I had a look at currently open inflight PRs and the conflicts should be minimal if I'm not overlooking something.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 82.12649% with 195 lines in your changes missing coverage. Please review.

Project coverage is 89.61%. Comparing base (4147de2) to head (bc122e3).

Files with missing lines	Patch %	Lines
lightning/src/util/test_channel_signer.rs	48.17%	8 Missing and 77 partials :warning:
lightning/src/util/test_utils.rs	84.01%	68 Missing and 2 partials :warning:
lightning/src/util/ser.rs	73.84%	17 Missing :warning:
lightning/src/util/ser_macros.rs	91.59%	9 Missing and 1 partial :warning:
lightning/src/util/wakers.rs	93.00%	5 Missing and 2 partials :warning:
lightning/src/util/transaction_utils.rs	95.71%	3 Missing and 3 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3323 +/- ## ========================================== - Coverage 89.66% 89.61% -0.06% ========================================== Files 126 126 Lines 103306 103912 +606 Branches 103306 103912 +606 ========================================== + Hits 92634 93118 +484 - Misses 7953 8027 +74 - Partials 2719 2767 +48 ```

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[TheBlueMatt]

Ugh, can we split this? 42 commits in one PR is just a lot...

[tnull]

Ugh, can we split this? 42 commits in one PR is just a lot...

Alright, happy to if you prefer (although at least half of these commits are one-line diffs). Now split out ~the first half of commits to #3324.

[tnull]

Rebased after https://github.com/lightningdevkit/rust-lightning/pull/3327 landed.

[tnull]

Rebased after #3324 landed.