Add Forms and Multipart evaluation tests and documentation

[Copilot]

Evaluates Java HTTP Client support for HTML form submissions (application/x-www-form-urlencoded) and multipart/form-data requests including file uploads.

Changes

Test Suites

• JavaHttpClientFormsTest - 4 tests demonstrating no built-in form API, manual URL encoding required
• JavaHttpClientMultipartTest - 5 tests demonstrating no built-in multipart API, manual boundary/header construction required

Test Infrastructure

• NettyFormsServer - Handles POST requests, parses form-urlencoded and multipart data for validation

Documentation

• FORMS_AND_MULTIPART.md - Analysis of missing APIs, comparison with Apache HttpClient/OkHttp, manual implementation requirements
• README.md - Updated with new test scenarios

Key Findings

Java HTTP Client provides no convenience APIs for forms or multipart. Developers must manually:

// Forms: Manual URL encoding required
String formData = data.entrySet().stream()
    .map(e -> URLEncoder.encode(e.getKey(), UTF_8) + "=" + 
              URLEncoder.encode(e.getValue(), UTF_8))
    .collect(Collectors.joining("&"));

HttpRequest.newBuilder()
    .header("Content-Type", "application/x-www-form-urlencoded")
    .POST(HttpRequest.BodyPublishers.ofString(formData))
    .build();

// Multipart: Manual boundary generation and part construction required
String boundary = "----WebKitFormBoundary" + System.currentTimeMillis();
byte[] body = buildMultipartBody(boundary, fields, files); // Complex manual construction

HttpRequest.newBuilder()
    .header("Content-Type", "multipart/form-data; boundary=" + boundary)
    .POST(HttpRequest.BodyPublishers.ofByteArray(body))
    .build();

Compare with other clients (Apache HttpClient MultipartEntityBuilder, OkHttp MultipartBody.Builder()).

Test Results: 9 tests added, all pass. No security vulnerabilities (CodeQL).

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Evaluation of Forms an Multiparts</issue_title>
<issue_description>## Forms

Convince Support for posting of form data to the server.

One can always do this if you’re willing to build up the request from scratch yourself, so what we’re really talking about here is whether a specific API is provided.

Multipart request and file upload

Support for sending multipart requests to the server, as with forms, we’re interested in whether the client provides an API specifically for this and how it can be improved</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Evaluation of Forms an Multiparts #20

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