parse: add integral-slice type parsing support

Support functions for integral-type slice-typed flags.

Support a simple comma-separated list of integers. Let
strconv.Parse{Int,Uint} pick the base so we naturally support Go's
format for binary, hex and octal.

Use generics so we only have one implementation for each of signed and
unsigned ints.

parse/integral_slice.go

@@ -0,0 +1,46 @@
+package parse
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"unsafe"
+)
+
+// SignedIntegralSlice splits on commas and parses into a slice of integers
+// Parses with strconv.ParseInt and the base set to 0 so base prefixes are available.
+// Whitespace is trimmed around the integers before parsing to allow for reasonable separtion (shell word-splitting aside)
+func SignedIntegralSlice[I int | int64 | int32 | int16 | int8](s string) ([]I, error) {
+	parts := strings.Split(s, ",")
+	out := make([]I, len(parts))
+
+	bitSize := int(unsafe.Sizeof(I(0)) * 8)
+
+	for i, p := range parts {
+		val, parseErr := strconv.ParseInt(strings.TrimSpace(p), 0, bitSize)
+		if parseErr != nil {
+			return nil, fmt.Errorf("failed to parse integer index %d: %w", i, parseErr)
+		}
+		out[i] = I(val)
+	}
+	return out, nil
+}
+
+// UnsignedIntegralSlice splits on commas and parses into a slice of integers
+// Parses with strconv.ParseInt and the base set to 0 so base prefixes are available.
+// Whitespace is trimmed around the integers before parsing to allow for reasonable separtion (shell word-splitting aside)
+func UnsignedIntegralSlice[I uint | uint64 | uint32 | uint16 | uint8 | uintptr](s string) ([]I, error) {
+	parts := strings.Split(s, ",")
+	out := make([]I, len(parts))
+
+	bitSize := int(unsafe.Sizeof(I(0)) * 8)
+
+	for i, p := range parts {
+		val, parseErr := strconv.ParseUint(strings.TrimSpace(p), 0, bitSize)
+		if parseErr != nil {
+			return nil, fmt.Errorf("failed to parse integer index %d: %w", i, parseErr)
+		}
+		out[i] = I(val)
+	}
+	return out, nil
+}