replace strings.Split(N) for strings.Cut() or alternatives

Go 1.18 and up now provides a strings.Cut() which is better suited for
splitting key/value pairs (and similar constructs), and performs better:

```go
func BenchmarkSplit(b *testing.B) {
        b.ReportAllocs()
        data := []string{"12hello=world", "12hello=", "12=hello", "12hello"}
        for i := 0; i < b.N; i++ {
                for _, s := range data {
                        _ = strings.SplitN(s, "=", 2)[0]
                }
        }
}

func BenchmarkCut(b *testing.B) {
        b.ReportAllocs()
        data := []string{"12hello=world", "12hello=", "12=hello", "12hello"}
        for i := 0; i < b.N; i++ {
                for _, s := range data {
                        _, _, _ = strings.Cut(s, "=")
                }
        }
}
```

    BenchmarkSplit
    BenchmarkSplit-10            8244206               128.0 ns/op           128 B/op          4 allocs/op
    BenchmarkCut
    BenchmarkCut-10             54411998                21.80 ns/op            0 B/op          0 allocs/op

While looking at occurrences of `strings.Split()`, I also updated some for alternatives,
or added some constraints; for cases where an specific number of items is expected, I used `strings.SplitN()`
with a suitable limit. This prevents (theoretical) unlimited splits.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/cap/cap_linux.go

@@ -80,15 +80,14 @@ func ParseProcPIDStatus(r io.Reader) (map[Type]uint64, error) {
 	scanner := bufio.NewScanner(r)
 	for scanner.Scan() {
 		line := scanner.Text()
-		pair := strings.SplitN(line, ":", 2)
-		if len(pair) != 2 {
+		k, v, ok := strings.Cut(line, ":")
+		if !ok {
 			continue
 		}
-		k := strings.TrimSpace(pair[0])
-		v := strings.TrimSpace(pair[1])
+		k = strings.TrimSpace(k)
 		switch k {
 		case "CapInh", "CapPrm", "CapEff", "CapBnd", "CapAmb":
-			ui64, err := strconv.ParseUint(v, 16, 64)
+			ui64, err := strconv.ParseUint(strings.TrimSpace(v), 16, 64)
 			if err != nil {
 				return nil, fmt.Errorf("failed to parse line %q", line)
 			}