Improve efficiency and fix cgroups

[protortyp]

Fixes some of the cgroups hardcoded paths, and improves efficiency by replacing Mutex<HashMap> with DashMap for faster read access, as write requests may be more rare.

[codecov]

Codecov Report

Attention: Patch coverage is 58.49057% with 22 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/mworker/src/worker.rs	0.00%	13 Missing ⚠️
crates/mbatch/src/main.rs	0.00%	9 Missing ⚠️

Files with missing lines	Coverage Δ
crates/cgroups/src/cgroups.rs	93.89% <100.00%> (+0.61%)	⬆️
crates/cgroups/src/cgroups_test.rs	90.94% <100.00%> (+0.05%)	⬆️
crates/melond/src/scheduler.rs	93.24% <ø> (+0.29%)	⬆️
crates/mbatch/src/main.rs	0.00% <0.00%> (ø)
crates/mworker/src/worker.rs	0.00% <0.00%> (ø)