build: modernize Go usage

This commit modernizes Go usage. This was done with:

go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -fix -test ./...

Then files needed to be `go fmt`ed and a few comments needed to be
restored.

The modernizations include replacing

- if/else conditional assignment by a call to the built-in min or max functions added in go1.21
- sort.Slice(x, func(i, j int) bool) { return s[i] < s[j] } by a call to slices.Sort(s), added in go1.21
- interface{} by the 'any' type added in go1.18
- append([]T(nil), s...) by slices.Clone(s) or slices.Concat(s), added in go1.21
- loop around an m[k]=v map update by a call to one of the Collect, Copy, Clone, or Insert functions from the maps package, added in go1.21
- []byte(fmt.Sprintf...) by fmt.Appendf(nil, ...), added in go1.19
- append(s[:i], s[i+1]...) by slices.Delete(s, i, i+1), added in go1.21
- a 3-clause for i := 0; i < n; i++ {} loop by for i := range n {}, added in go1.22

backend/crypt/cipher.go

@@ -192,7 +192,7 @@ func newCipher(mode NameEncryptionMode, password, salt string, dirNameEncrypt bo
 		dirNameEncrypt:  dirNameEncrypt,
 		encryptedSuffix: ".bin",
 	}
-	c.buffers.New = func() interface{} {
+	c.buffers.New = func() any {
 		return new([blockSize]byte)
 	}
 	err := c.Key(password, salt)
@@ -336,7 +336,7 @@ func (c *Cipher) obfuscateSegment(plaintext string) string {
 	_, _ = result.WriteString(strconv.Itoa(dir) + ".")
 
 	// but we'll augment it with the nameKey for real calculation
-	for i := 0; i < len(c.nameKey); i++ {
+	for i := range len(c.nameKey) {
 		dir += int(c.nameKey[i])
 	}
 
@@ -418,7 +418,7 @@ func (c *Cipher) deobfuscateSegment(ciphertext string) (string, error) {
 	}
 
 	// add the nameKey to get the real rotate distance
-	for i := 0; i < len(c.nameKey); i++ {
+	for i := range len(c.nameKey) {
 		dir += int(c.nameKey[i])
 	}
 
@@ -664,7 +664,7 @@ func (n *nonce) increment() {
 // add a uint64 to the nonce
 func (n *nonce) add(x uint64) {
 	carry := uint16(0)
-	for i := 0; i < 8; i++ {
+	for i := range 8 {
 		digit := (*n)[i]
 		xDigit := byte(x)
 		x >>= 8