Optimize recursive ls (#2083)

* ls: Remove allocations by eliminating collect/clones

* ls: Introduce PathData structure

- PathData will hold Path related metadata / strings that are required
frequently in subsequent functions
- All data is precomputed and cached and subsequent functions just
use cached data

* ls: Cache more data related to paths

- Cache filename and sort by filename instead of full path
- Cache uid->usr and gid->grp mappings
https://github.com/uutils/coreutils/pull/2099/files
* ls: Add BENCHMARKING.md

* ls: Document PathData structure

* tests/ls: Add testcase for error paths with width option

* ls: Fix unused import warning

cached will be only used for unix currently as current use of
caching gid/uid mappings is only relevant on unix

* ls: Suggest checking syscall count in BENCHMARKING.md

* ls: Remove mentions of sort in BENCHMARKING.md

* ls: Remove dependency on cached

Implement caching using HashMap and lazy_static

* ls: Fix MSRV error related to map_or

Rust 1.40 did not support map_or for result types

tests/by-util/test_ls.rs

@@ -103,6 +103,14 @@ fn test_ls_width() {
             .succeeds()
             .stdout_only("test-width-1\ntest-width-2\ntest-width-3\ntest-width-4\n");
     }
+
+    for option in &["-w 1a", "-w=1a", "--width=1a", "--width 1a"] {
+        scene
+            .ucmd()
+            .args(&option.split(" ").collect::<Vec<_>>())
+            .fails()
+            .stderr_only("ls: error: invalid line width: ‘1a’");
+    }
 }
 
 #[test]