Allow user to force codspeed root dir value and to install google_benchmark as a system lib

[GuillaumeLagrange]

No description provided.

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #10 will not alter performance

_{Comparing allow-codspeed-intallation (308c879) with main (5324618)}

Summary

✅ 42 untouched benchmarks

[codspeed-hq]

CodSpeed Walltime Performance Report

Merging #10 will degrade performances by 33.33%

_{Comparing allow-codspeed-intallation (308c879) with main (5324618)}

Summary

⚡ 3 improvements
❌ 4 regressions
✅ 35 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	BarTest[MyFixture]	< 1 ns	< 1 ns	+20%
❌	DoubleTest[MyTemplatedFixture, double]	< 1 ns	< 1 ns	-20%
❌	IntTest[MyTemplatedFixture, int]	< 1 ns	< 1 ns	-16.67%
⚡	BM_Capture[int_string_test]	< 1 ns	< 1 ns	+50%
❌	BM_Capture[int_test]	< 1 ns	< 1 ns	-33.33%
⚡	BM_rand_vector	< 1 ns	< 1 ns	+25%
❌	BM_Template1_Capture[int_string_test]	< 1 ns	< 1 ns	-16.67%

[art049]

is this comment necessary? not sure to understand

[GuillaumeLagrange]

oups, that's a claude leftover sorry 🤓

[art049]

or go to jail