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_test.go

@@ -1307,10 +1307,7 @@ func TestNewDecrypterSeekLimit(t *testing.T) {
 	open := func(ctx context.Context, underlyingOffset, underlyingLimit int64) (io.ReadCloser, error) {
 		end := len(ciphertext)
 		if underlyingLimit >= 0 {
-			end = int(underlyingOffset + underlyingLimit)
-			if end > len(ciphertext) {
-				end = len(ciphertext)
-			}
+			end = min(int(underlyingOffset+underlyingLimit), len(ciphertext))
 		}
 		reader = io.NopCloser(bytes.NewBuffer(ciphertext[int(underlyingOffset):end]))
 		return reader, nil
@@ -1490,7 +1487,7 @@ func TestDecrypterRead(t *testing.T) {
 	assert.NoError(t, err)
 
 	// Test truncating the file at each possible point
-	for i := 0; i < len(file16)-1; i++ {
+	for i := range len(file16) - 1 {
 		what := fmt.Sprintf("truncating to %d/%d", i, len(file16))
 		cd := newCloseDetector(bytes.NewBuffer(file16[:i]))
 		fh, err := c.newDecrypter(cd)