improve parsing of values with units (#9190)

closes #9111 

# Description

this pr improves parsing of values with units (`filesizes`, `durations`
and any other **future values**) by:

1. allowing underscores in the value part
```nu
> 42kb          # okay
> 42_sec        # okay
> 1_000_000mib  # okay
> 69k_b         # not okay, underscores not allowed in the unit
```

2. improving error messages involving these values
```nu
> sleep 40-sec

# before
Error: nu::parser::parse_mismatch

  × Parse mismatch during operation.
   ╭─[entry #42:1:1]
 1 │ sleep 40-sec
   ·       ──┬──
   ·         ╰── expected duration with valid units
   ╰────

# now
Error:
  × duration value must be a number
   ╭─[entry #41:1:1]
 1 │ sleep 40-sec
   ·       ─┬─
   ·        ╰── not a number
   ╰────
```

3. unifying parsing of these values. now all of these use one function

# User-Facing Changes

filesizes and durations can now have underscores for readability

src/tests/test_parser.rs

@@ -526,3 +526,38 @@ fn extern_errors_with_no_space_between_params_and_name_1() -> TestResult {
 fn extern_errors_with_no_space_between_params_and_name_2() -> TestResult {
     fail_test("extern cmd(--flag)", "expected space")
 }
+
+#[test]
+fn duration_with_underscores_1() -> TestResult {
+    run_test("420_min", "7hr")
+}
+
+#[test]
+fn duration_with_underscores_2() -> TestResult {
+    run_test("1_000_000sec", "1wk 4day 13hr 46min 40sec")
+}
+
+#[test]
+fn duration_with_underscores_3() -> TestResult {
+    fail_test("1_000_d_ay", "executable was not found")
+}
+
+#[test]
+fn duration_with_faulty_number() -> TestResult {
+    fail_test("sleep 4-ms", "duration value must be a number")
+}
+
+#[test]
+fn filesize_with_underscores_1() -> TestResult {
+    run_test("420_mb", "400.5 MiB")
+}
+
+#[test]
+fn filesize_with_underscores_2() -> TestResult {
+    run_test("1_000_000B", "976.6 KiB")
+}
+
+#[test]
+fn filesize_with_underscores_3() -> TestResult {
+    fail_test("42m_b", "executable was not found")
+}