Represent runtime fixture failure causality

[MatthewMckee4]

Summary

Represent runtime fixture setup failures as typed test-result causality, preserving shared root diagnostics while identifying required, use_fixtures, and auto-use relationships across terminal, JUnit, JSON, and JSONL output. Closes #1078.

Test Plan

Ran focused fixture and result-report integration tests, workspace Clippy, and uvx prek run -a.

[github-actions]

⚡ Merging this PR improves performance

All benchmark scores

	Mode	Benchmark	Base	Head	Change	Runs
✅	WallTime	requests	16.055 s	16.054 s	-0.0%	4
✅	WallTime	fastapi	6.352 s	6.346 s	-0.1%	7
✅	WallTime	httpx	9.233 s	9.192 s	-0.4%	7
⚡	WallTime	h11	338.9 ms	319.8 ms	-5.6%	21
✅	WallTime	markupsafe	241.4 ms	242.0 ms	+0.3%	21
✅	WallTime	sniffio	282.7 ms	283.0 ms	+0.1%	21
✅	WallTime	itsdangerous	250.9 ms	250.6 ms	-0.1%	21
✅	WallTime	blinker	236.5 ms	236.4 ms	-0.0%	21
⚡	WallTime	jinja	577.6 ms	558.8 ms	-3.3%	21
✅	WallTime	installer	285.4 ms	284.9 ms	-0.2%	21
✅	WallTime	tomlkit	580.2 ms	579.4 ms	-0.2%	15
✅	WallTime	outcome	280.8 ms	281.3 ms	+0.2%	21
✅	WallTime	pluggy	259.5 ms	258.5 ms	-0.4%	21
✅	WallTime	werkzeug	8.842 s	8.825 s	-0.2%	7

[github-actions]

✅ Merging this PR will not alter memory usage

All benchmark scores

	Mode	Benchmark	Base	Head	Change	Runs
✅	Memory	requests	60.2 MiB	60.4 MiB	+0.2%	4
✅	Memory	fastapi	146.2 MiB	146.5 MiB	+0.2%	7
✅	Memory	httpx	81.0 MiB	81.2 MiB	+0.2%	7
✅	Memory	h11	53.2 MiB	53.4 MiB	+0.3%	21
✅	Memory	markupsafe	41.9 MiB	42.0 MiB	+0.1%	21
✅	Memory	sniffio	47.5 MiB	47.8 MiB	+0.5%	21
✅	Memory	itsdangerous	44.2 MiB	44.4 MiB	+0.5%	21
✅	Memory	blinker	46.9 MiB	46.9 MiB	+0.0%	21
✅	Memory	jinja	56.9 MiB	57.1 MiB	+0.3%	21
✅	Memory	installer	48.7 MiB	48.9 MiB	+0.4%	21
✅	Memory	tomlkit	49.1 MiB	49.3 MiB	+0.4%	15
✅	Memory	outcome	48.6 MiB	48.7 MiB	+0.2%	21
✅	Memory	pluggy	45.9 MiB	46.2 MiB	+0.6%	21
✅	Memory	werkzeug	136.7 MiB	136.7 MiB	+0.0%	7

[github-actions]

✅ No diagnostic changes

Test result comparison

Project	Previous	New
requests	❌ 149 pass · 0 fail · 6 error · 12 skip	❌ 149 pass · 0 fail · 6 error · 12 skip
fastapi	❌ 1596 pass · 7 fail · 434 error · 1 skip	❌ 1596 pass · 7 fail · 434 error · 1 skip
httpx	❌ 1022 pass · 50 fail · 54 error · 1 skip	❌ 1022 pass · 50 fail · 54 error · 1 skip
h11	✅ 78 pass · 0 fail · 0 error · 0 skip	✅ 78 pass · 0 fail · 0 error · 0 skip
markupsafe	❌ 0 pass · 0 fail · 26 error · 0 skip	❌ 0 pass · 0 fail · 26 error · 0 skip
sniffio	✅ 3 pass · 0 fail · 0 error · 1 skip	✅ 3 pass · 0 fail · 0 error · 1 skip
itsdangerous	✅ 10 pass · 0 fail · 0 error · 0 skip	✅ 10 pass · 0 fail · 0 error · 0 skip
blinker	✅ 25 pass · 0 fail · 0 error · 0 skip	✅ 25 pass · 0 fail · 0 error · 0 skip
jinja	❌ 135 pass · 0 fail · 16 error · 0 skip	❌ 135 pass · 0 fail · 16 error · 0 skip
installer	✅ 20 pass · 0 fail · 0 error · 0 skip	✅ 20 pass · 0 fail · 0 error · 0 skip
tomlkit	✅ 332 pass · 0 fail · 0 error · 0 skip	✅ 332 pass · 0 fail · 0 error · 0 skip
outcome	✅ 10 pass · 0 fail · 0 error · 0 skip	✅ 10 pass · 0 fail · 0 error · 0 skip
pluggy	❌ 124 pass · 1 fail · 27 error · 0 skip	❌ 124 pass · 1 fail · 27 error · 0 skip
werkzeug	❌ 728 pass · 3 fail · 0 error · 0 skip	❌ 728 pass · 3 fail · 0 error · 0 skip