all: use Go 1.26 things, run most gofix modernizers

I omitted a lot of the min/max modernizers because they didn't
result in more clear code.

Some of it's older "for x := range 123".

Also: errors.AsType, any, fmt.Appendf, etc.

Updates #18682

Change-Id: I83a451577f33877f962766a5b65ce86f7696471c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

drive/driveimpl/compositedav/rewriting.go

@@ -63,7 +63,7 @@ func (h *Handler) delegateRewriting(w http.ResponseWriter, r *http.Request, path
 
 	// Fixup paths to add the requested path as a prefix, escaped for inclusion in XML.
 	pp := shared.EscapeForXML(shared.Join(pathComponents[0:mpl]...))
-	b := responseHrefRegex.ReplaceAll(bw.buf.Bytes(), []byte(fmt.Sprintf("$1<D:href>%s/$3</D:href>", pp)))
+	b := responseHrefRegex.ReplaceAll(bw.buf.Bytes(), fmt.Appendf(nil, "$1<D:href>%s/$3</D:href>", pp))
 	return bw.status, b
 }