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Summary

Enable frozen-string-literal checks across the MRI and JRuby CI matrix, and fix the JRuby buffer mutations exposed by those checks.

Changes

• Add JRuby 10.1 and jruby-head to the shared Ruby CI matrix, using Temurin 25.
• Run nested JRuby-specific tests through Rake alongside the rest of the suite.
• Keep JRuby socket and PEM working buffers mutable, and avoid mutating caller-owned binary strings during debug logging.
• Address CI warnings in test code and load WEBrick HTTPS before the JRuby request patch to preserve the original parser.

Validation

• GitHub Actions: all 12 matrix jobs passed; Ruby 2.5 passed on retry after an intermittent segfault in the SSL test suite.
• JRuby 10.1.2.0 with Temurin 25: all 256 tests passed in two consecutive full-suite runs.