feat: harden curl_parser, tolerate flags, improve output, and expand tests

- Pre-filter unknown flags before ArgParser; keep positional args.
- Tolerate non-request flags: -v/--verbose, --connect-timeout, --retry, --output, --compressed, -i/--include, --globoff.
- Auth: support --oauth2-bearer; map to - Authorization only if absent.
- Cookies: parse -b/--cookie; accept -c/--cookie-jar (ignored for request).
- URL: prefer first http(s) positional when --url missing; quote cleaning.
- Data: merge data-urlencode → data-raw → data-binary → data; default POST when body/form present; HEAD remains HEAD.
- Forms: parse -F entries; auto-set multipart Content-Type if missing.
- Headers: robust -H parsing for multi-colon values.
- toCurlString: deterministic order; fix continuation spacing; emit -d right after headers/form; place -k/-L at end.
- Utils: normalize backslash-newlines/CRLF; remove stray '+'; shlex split.
- Tests: add unknown flags, oauth2-bearer (and non-override), cookie-jar, verbose/timeout/retry/output tolerance, data merging order, HEAD+data, -A user-agent, -b filename.
- Docs: add Dartdoc for utils; class docs present.

packages/curl_parser/test/dart_to_curl_test.dart

@@ -117,9 +117,46 @@ void main() {
  -F "token=123"''',
         );
       });
+
+      test('form defaults header when absent', () {
+        final curl = Curl(
+          method: 'POST',
+          uri: Uri.parse('https://api.apidash.dev/io/img'),
+          form: true,
+          formData: [
+            FormDataModel(
+              name: 'file',
+              value: '/tmp/a.png',
+              type: FormDataType.file,
+            ),
+          ],
+        );
+        // parse back to ensure header gets defaulted in parser
+        final parsed = Curl.parse(curl.toCurlString());
+        expect(parsed.form, isTrue);
+        expect(
+            parsed.headers?[kHeaderContentType] ??
+                parsed.headers?['content-type'],
+            'multipart/form-data');
+      });
     },
   );
 
+  group('Roundtrip with body', () {
+    test('toCurlString includes body when present', () {
+      final curl = Curl(
+        method: 'POST',
+        uri: Uri.parse('https://api.apidash.dev/submit'),
+        data: 'a=1&b=2',
+      );
+      final s = curl.toCurlString();
+      final back = Curl.parse(s);
+      expect(back.method, 'POST');
+      expect(back.data, 'a=1&b=2');
+      expect(back.uri, Uri.parse('https://api.apidash.dev/submit'));
+    });
+  });
+
   group(
     'Special Parameters',
     () {