userland: search and exec tools, spawn library (T14)

rg (ripgrep 15.2), grep (ours, on ripgrep's regex crates), find and xargs
(ours), sed (uutils 0.3 wrapper), diff and cmp (uutils diffutils 0.6 with -r),
fd 10.5, jaq 2.3, env and timeout. userland/spawn is a small Command-like
client of the process interface. search-test.nu: 42 cases match native tools.

userland/diffutils/src/macros.rs

@@ -0,0 +1,25 @@
+// asserts equality of the actual diff and expected diff
+// considering datetime varitations
+//
+// It replaces the modification time in the actual diff
+// with placeholder "TIMESTAMP" and then asserts the equality
+//
+// For eg.
+// let brief = "*** fruits_old.txt\t2024-03-24 23:43:05.189597645 +0530\n
+//              --- fruits_new.txt\t2024-03-24 23:35:08.922581904 +0530\n";
+//
+// replaced = "*** fruits_old.txt\tTIMESTAMP\n
+//             --- fruits_new.txt\tTIMESTAMP\n";
+#[macro_export]
+macro_rules! assert_diff_eq {
+    ($actual:expr, $expected:expr) => {{
+        use regex::Regex;
+        use std::str;
+
+        let diff = str::from_utf8(&$actual).unwrap();
+        let re = Regex::new(r"\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}\.\d+ [+-]\d{4}").unwrap();
+        let actual = re.replacen(diff, 2, "TIMESTAMP");
+
+        assert_eq!(actual, $expected);
+    }};
+}