fix: consolidate split-package-names

[wraithgar]

It was only ever used by npm edit so it's inline now.
Rewrote npm edit tests to be real

[npm-robot]

found 1 benchmarks with statistically significant performance improvements

• app-large: no-cache

timing results

app-large	clean	lock-only	cache-only	cache-only peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit
npm@8	68.777 ±5.20	36.050 ±0.35	20.428 ±0.79	24.471 ±0.81	3.435 ±0.01	3.507 ±0.09	2.815 ±0.07	13.600 ±0.08	2.853 ±0.13	3.733 ±0.01
#4632	63.316 ±3.96	34.633 ±0.94	19.649 ±0.16	22.667 ±1.01	3.357 ±0.19	3.178 ±0.15	2.501 ±0.03	13.062 ±0.19	2.694 ±0.01	3.740 ±0.26

app-medium	clean	lock-only	cache-only	cache-only peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit
npm@8	47.036 ±7.25	26.792 ±0.50	14.866 ±0.46	15.660 ±0.47	3.016 ±0.03	2.884 ±0.04	2.608 ±0.06	9.589 ±0.06	2.364 ±0.02	3.501 ±0.12
#4632	53.515 ±11.93	28.540 ±0.01	15.903 ±0.01	16.669 ±0.09	3.162 ±0.06	3.129 ±0.06	2.786 ±0.06	9.929 ±0.13	2.541 ±0.10	3.488 ±0.06

[lukekarrys]

Approved with one question that I was curious about.

[lukekarrys]

Previously spawk was calling clean after the teardown of some invididual tests. Is that the same thing as calling spawk.done() in afterEach and then spawk.unload() once at the end of all the tests?