[NicolasDorier]

Summary

• Add stable Bitcoin Core 32.1 downloads for Linux, macOS, and Windows with official SHA-256 checksums.
• Preserve the existing 32.0rc4 entry and use 32.1 for tests selecting the latest Bitcoin Core version.
• Bump NBitcoin.TestFramework from 5.0.6 to 5.0.7.

Bitcoin Core 32.0 was tagged but never fully released; 32.1 supersedes it.

Validation

• Build the .NET 10 test project successfully in Release configuration.
• Verify all three download checksums against the official 32.1 SHA256SUMS.
• Download and start the Linux binary through the test framework; confirm bitcoind reports v32.1.0.
• Pass all 58 RPCClient integration tests locally against Bitcoin Core 32.1, including CanUseCore32RPCs.

Package publication will be performed separately after merge.