refactor(HttpClient): Remove HttpClient library

[hirokiterashima]

Summary

This PR replaces usages of the legacy, end-of-life org.apache.httpcomponents:httpclient (4.5.14) library with Spring's modern, built-in RestClient (available in Spring Boot 3.3.x via spring-boot-starter-web) and removes the dependency from pom.xml.

Motivation

• Security & Maintenance: Apache HttpClient 4.x reached End-of-Life (EOL) in late 2022 and will not receive future security patches or maintenance.
• Spring Boot 3 Alignment: Spring 6 / Spring Boot 3 dropped support for Apache HttpClient 4.x. Spring now provides RestClient as an idiomatic, fluent synchronous HTTP client backed by Java 11+ java.net.http.HttpClient out of the box without requiring third-party dependencies.
• Dependency Reduction: Eliminating httpclient reduces the external dependency footprint.

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Changes

1. Dependency Removal

• pom.xml: Removed org.apache.httpcomponents:httpclient (4.5.14).

2. Service & Controller Migrations

• CRaterService.java:
  • Injected RestClient.Builder and Environment via constructor.
  • Replaced Apache HttpClient, HttpPost, and manual Base64 Basic Authentication header encoding with RestClient's fluent API (.headers(h -> h.setBasicAuth(...))).
  • Configured MediaType.APPLICATION_JSON_UTF8 (application/json;charset=utf-8) as required by the CRater scoring endpoint.
  • Replaced entity stream reading with .retrieve().body(String.class).
• ContactAPIController.java:
  • Replaced HttpPost, NameValuePair, UrlEncodedFormEntity, and manual BufferedReader stream reading with RestClient and LinkedMultiValueMap.
• DailyAdminJob.java:
  • Replaced HttpClient, HttpPost, and manual connection release in postStatistics with RestClient and LinkedMultiValueMap.
  • Cleaned up unused imports.

3. Test Improvements

• CRaterServiceTest.java:
  • Updated the test setup to use Spring Test's MockRestServiceServer.
  • Mocked the HTTP POST requests across all 4 unit tests to prevent actual network calls to test.org and eliminate Fatal transport error connection exceptions in test logs.

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Verification

• Full compilation passes: mvn test-compile
• Unit tests pass without network errors or exceptions:
  • mvn test -Dtest=CRaterServiceTest (4/4 passed)
  • mvn test -Dtest=CRaterControllerTest (4/4 passed)
• Verified zero remaining imports or references to org.apache.http in the codebase.

[hirokiterashima]

🎉 This PR is included in version 1.25.3 🎉

The release is available on GitHub release

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