feat(llar): add install command wrapper

[MeteorsLiu]

Add a Go wrapper for invoking the LLAR install command from LLGo.

The implementation includes:

• Add llar.New(bin, verbose) and Cmd.Install for executing llar install.
• Add typed Module, Config, Dependency, and Result values without importing the LLAR module.
• Map optional output, target matrix fields, repeated options, and verbose stderr forwarding to the CLI.
• Add fake-command tests for argument generation, optional output, JSON decoding, and command failures.

This gives LLGo a typed, testable entry point for installing LLAR modules while keeping the existing CLI as the execution boundary.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[github-actions]

LLGo baseline benchmarks

5de100a51be0 | workflow run | long-term charts

Program measurements

Platform	Workload	File size	vs base	Text size	vs base	Build	vs base	Run	vs base
Linux	cprintf	19256 B	0 B / +0.0%	387 B	0 B / +0.0%	341.826 ms	+429 us / +0.1% (worse)	1.278 ms	-3.985 us / -0.3% (better)
Linux	cprintf-lto	19088 B	0 B / +0.0%	368 B	0 B / +0.0%	349.616 ms	-3.775 ms / -1.1% (better)	1.252 ms	-83.25 us / -6.2% (better)
Linux	fmtprintf	1653232 B	0 B / +0.0%	501083 B	0 B / +0.0%	2.901 s	-39.4 ms / -1.3% (better)	3.346 ms	-15.2 us / -0.5% (better)
Linux	fmtprintf-lto	1525824 B	0 B / +0.0%	459700 B	0 B / +0.0%	9.145 s	-36.75 ms / -0.4% (better)	3.106 ms	-13.99 us / -0.4% (better)
Linux	println	62032 B	0 B / +0.0%	15261 B	0 B / +0.0%	341.970 ms	-7.466 ms / -2.1% (better)	1.617 ms	+20.32 us / +1.3% (worse)
Linux	println-lto	53840 B	0 B / +0.0%	12882 B	0 B / +0.0%	525.624 ms	-23.65 ms / -4.3% (better)	1.601 ms	-41.34 us / -2.5% (better)
macOS	cprintf	84480 B	0 B / +0.0%	16493 B	0 B / +0.0%	441.957 ms	-282.7 ms / -39.0% (better)	3.924 ms	-2.902 ms / -42.5% (better)
macOS	cprintf-lto	100704 B	0 B / +0.0%	16473 B	0 B / +0.0%	609.779 ms	-129.8 ms / -17.5% (better)	4.143 ms	-1.428 ms / -25.6% (better)
macOS	fmtprintf	1498256 B	0 B / +0.0%	882133 B	0 B / +0.0%	4.584 s	+1.055 s / +29.9% (worse)	8.855 ms	+3.473 ms / +64.5% (worse)
macOS	fmtprintf-lto	1208976 B	0 B / +0.0%	875129 B	0 B / +0.0%	8.106 s	-443.6 ms / -5.2% (better)	6.593 ms	+556.9 us / +9.2% (worse)
macOS	println	114832 B	0 B / +0.0%	34849 B	0 B / +0.0%	432.783 ms	-274.5 ms / -38.8% (better)	3.646 ms	-468.7 us / -11.4% (better)
macOS	println-lto	118656 B	0 B / +0.0%	32489 B	0 B / +0.0%	535.525 ms	-299.3 ms / -35.8% (better)	3.781 ms	-1.855 ms / -32.9% (better)

Core language and compiler benchmarks

Platform	Benchmark	ns/op	vs base
Linux	BenchmarkLookupPCRandom	13.240 ns/op	-0.16 ns/op / -1.2% (better)
Linux	BenchmarkMergeCompilerFlags	151.300 ns/op	-0.6 ns/op / -0.4% (better)
Linux	BenchmarkMergeLinkerFlags	94.860 ns/op	-0.26 ns/op / -0.3% (better)
Linux	BenchmarkChannelBuffered	35.520 ns/op	-0.02 ns/op / -0.1% (better)
Linux	BenchmarkChannelHandoff	28778 ns/op	+1292 ns/op / +4.7% (worse)
Linux	BenchmarkDefer	49.780 ns/op	-1.2 ns/op / -2.4% (better)
Linux	BenchmarkDirectCall	1.557 ns/op	0 ns/op / +0.0%
Linux	BenchmarkGlobalRead	1.870 ns/op	-0.002 ns/op / -0.1% (better)
Linux	BenchmarkGlobalWrite	2.481 ns/op	-0.003 ns/op / -0.1% (better)
Linux	BenchmarkGoroutine	32434 ns/op	-178 ns/op / -0.5% (better)
Linux	BenchmarkInterfaceCall	8.414 ns/op	0 ns/op / +0.0%
Linux	BenchmarkRuntimeGetG	2.181 ns/op	+0.001 ns/op / +0.04587% (worse)
macOS	BenchmarkLookupPCRandom	13.410 ns/op	-0.77 ns/op / -5.4% (better)
macOS	BenchmarkMergeCompilerFlags	147.600 ns/op	-35.6 ns/op / -19.4% (better)
macOS	BenchmarkMergeLinkerFlags	105.400 ns/op	-4.6 ns/op / -4.2% (better)
macOS	BenchmarkChannelBuffered	30.110 ns/op	-3.78 ns/op / -11.2% (better)
macOS	BenchmarkChannelHandoff	7902 ns/op	+1221 ns/op / +18.3% (worse)
macOS	BenchmarkDefer	43.840 ns/op	-4.31 ns/op / -9.0% (better)
macOS	BenchmarkDirectCall	1.359 ns/op	-0.121 ns/op / -8.2% (better)
macOS	BenchmarkGlobalRead	1.185 ns/op	-0.148 ns/op / -11.1% (better)
macOS	BenchmarkGlobalWrite	1.445 ns/op	-0.153 ns/op / -9.6% (better)
macOS	BenchmarkGoroutine	52811 ns/op	-10704 ns/op / -16.9% (better)
macOS	BenchmarkInterfaceCall	6.296 ns/op	-0.508 ns/op / -7.5% (better)
macOS	BenchmarkRuntimeGetG	2.205 ns/op	-0.862 ns/op / -28.1% (better)

Compared with 6fe8babd468c measured in the same runner job.