Minor Reader tweaks

1- Remove `parser.trim`, it was only being used in 1 place. All other places
   are using `std.mem.trim(u8, X, &std.ascii.whitespace)`, so i updated MIME to
   use this as well

2- Use slightly more meaningful field name, i => pos, s = data

3- Leverage std.mem.indexOfScalarPos which can be more efficient for longer
   inputs (since it leverages SIMD)

src/url/query.zig

@@ -199,12 +199,12 @@ pub fn parseQuery(alloc: std.mem.Allocator, s: []const u8) !Values {
     const ln = s.len;
     if (ln == 0) return values;
 
-    var r = Reader{ .s = s };
+    var r = Reader{ .data = s };
     while (true) {
         const param = r.until('&');
         if (param.len == 0) break;
 
-        var rr = Reader{ .s = param };
+        var rr = Reader{ .data = param };
         const k = rr.until('=');
         if (k.len == 0) continue;