enable and fix stricter clippy linting

- add clippy to .build.yml to run on sr.ht
- add missing docs
- use core:: instead of std:: where possible
- use hypot() and mul_add() for better numeric stability
- make all float tests use asser_approx_eq() and explicitly check for NaN/Inf
- add missing semicolons here and there
- add #[must_use] to ensure caller uses returned value
- add const fn where appropriate
- change visibility from pub(crate) to pub (in private modules)

Signed-off-by: Stephen Waits <steve@waits.net>

proptest-regressions/height_vector.txt

@@ -8,3 +8,4 @@ cc 4a5cb6ca844d5306203ae00a99375c83a20ddf4ca427f0ae0b541697efa3d9b7 # shrinks to
 cc 38ed1e2c313317809f5469d856d2c1c61e4851c64a156cd1bdd0757fa7c77128 # shrinks to x = 0.0, y = -0.0, h = 0.0, m = -0.0
 cc b7d1b5e9fe3e33066b583c4532865373179972e9b5786ecc62438f23bc939e87 # shrinks to x = -0.0, y = 0.0, h = -3.448118e-33, m = -0.0
 cc 3c4fc4f21c82ffe5bcbc740ca9ab598e0894226acb86a3046a3a24cbbcdbf8e6 # shrinks to x = 0.0, y = 0.0, h = -0.0
+cc d1a551d7eb92bf69e3d0cd0b677baac5aaa5a95d6a016fccf67cf57af71c8b0c # shrinks to x = -5.098216e26, y = 0.0, h = 0.0