Optimize stroke cache and benchmark configurations

- Updated stroke cache to use parallel processing for pixel checks.
- Modified benchmark commands in notlar.txt to ensure consistent output and baseline comparisons.
- Created a plan for merging criterion directories and optimizing benchmark performance, including pre-allocation of buffers and various optimization strategies.
- Removed redundant output directory settings in benchmark files and ensured all benchmarks write to a single criterion directory.
- Updated documentation to reflect changes in benchmark paths and configurations.

.cargo/config.toml

@@ -1,6 +1,7 @@
 [env]
 PKG_CONFIG_PATH = "/tmp/dav1d-dev/usr/lib/x86_64-linux-gnu/pkgconfig"
 LIBRARY_PATH = "/tmp/dav1d-dev/usr/lib/x86_64-linux-gnu"
+CRITERION_HOME = { value = "criterion", relative = true }
 
 [target.x86_64-unknown-linux-gnu]
 rustflags = ["-C", "link-arg=-fuse-ld=mold"]