Add structured diff highlighting

[fabpot]

This adds structured unified and Git diff highlighting.

It handles metadata, file and hunk headers, combined-diff status columns, changed and context lines, and special markers using language-scoped tokens and linear parsing.

[github-actions]

Benchmark Results

Comparison of fix/diff-terminal-highlighting against main (a65bd95f70d01e082285e3c3f01cc33b6ddac1dd).

Open to see the benchmark results

benchmark	subject	set	revs	its	mem_peak	mode	rstdev
HighlighterBench	benchParse	apache	100	5	2.066mb +0.21%	73.482270μs +1.23%	±1.47% +69.29%
HighlighterBench	benchParse	bash	100	5	2.097mb +0.20%	205.892877μs +0.26%	±0.95% +48.61%
HighlighterBench	benchParse	bbcode	100	5	2.054mb +0.21%	74.936575μs -0.65%	±0.45% -4.59%
HighlighterBench	benchParse	blade	100	5	2.670mb +0.16%	1,084.493053μs -0.64%	±0.95% +44.41%
HighlighterBench	benchParse	css	100	5	2.084mb +0.20%	141.552114μs -0.11%	±0.48% -44.85%
HighlighterBench	benchParse	diff	100	5	2.049mb +2.13%	97.368219μs +261.64%	±1.04% -12.64%
HighlighterBench	benchParse	dockerfile	100	5	2.066mb +0.21%	88.645225μs -0.08%	±2.37% +243.82%
HighlighterBench	benchParse	dotenv	100	5	2.070mb +0.21%	76.989472μs -0.38%	±0.29% -51.38%
HighlighterBench	benchParse	gdscript	100	5	2.164mb +0.20%	333.823268μs -0.31%	±0.71% -17.30%
HighlighterBench	benchParse	graphql	100	5	2.085mb +0.20%	155.401722μs +1.64%	±2.47% +30.58%
HighlighterBench	benchParse	html	100	5	2.088mb +0.20%	117.798200μs +0.52%	±0.77% +14.44%
HighlighterBench	benchParse	http	100	5	2.058mb +0.21%	24.430548μs +0.70%	±1.63% +194.59%
HighlighterBench	benchParse	ini	100	5	2.073mb +0.20%	87.204247μs -0.60%	±0.87% -12.40%
HighlighterBench	benchParse	javascript	100	5	2.152mb +0.20%	272.574168μs -0.21%	±0.28% -80.20%
HighlighterBench	benchParse	json	100	5	2.127mb +0.20%	240.961977μs +0.15%	±0.98% +41.87%
HighlighterBench	benchParse	markdown	100	5	2.075mb +0.20%	76.028904μs -0.03%	±0.41% -30.84%
HighlighterBench	benchParse	nginx	100	5	2.139mb +0.20%	268.652877μs +0.19%	±0.50% +24.26%
HighlighterBench	benchParse	php	100	5	2.431mb +0.17%	756.136947μs -0.59%	±1.83% +126.30%
HighlighterBench	benchParse	python	100	5	2.328mb +0.18%	423.174716μs -0.68%	±0.78% +82.99%
HighlighterBench	benchParse	scss	100	5	2.100mb +0.20%	183.216223μs +0.10%	±1.10% +46.14%
HighlighterBench	benchParse	sql	100	5	2.099mb +0.20%	158.435264μs -0.18%	±0.47% +15.87%
HighlighterBench	benchParse	svelte	100	5	2.301mb +0.33%	1,081.087926μs -0.28%	±1.38% +13.11%
HighlighterBench	benchParse	terminal	100	5	2.094mb +0.20%	188.404462μs -0.38%	±0.46% +35.74%
HighlighterBench	benchParse	terraform	100	5	2.099mb +0.20%	175.525382μs +0.43%	±1.00% -40.50%
HighlighterBench	benchParse	typescript	100	5	2.525mb +0.17%	253.350489μs +1.72%	±0.67% -6.80%
HighlighterBench	benchParse	txt	100	5	2.045mb 0.00%	8.597280μs +0.58%	±0.92% -55.05%
HighlighterBench	benchParse	twig	100	5	19.206mb +0.02%	1,476.884618μs -1.17%	±0.53% -59.58%
HighlighterBench	benchParse	vue	100	5	2.382mb +0.18%	414.760568μs -0.22%	±0.33% -68.34%
HighlighterBench	benchParse	xml	100	5	2.102mb +0.20%	180.225910μs +0.08%	±0.37% -30.75%
HighlighterBench	benchParse	yaml	100	5	2.160mb +0.20%	321.749119μs -0.38%	±0.27% -27.62%

_{Generated by phpbench against commit f555969}