Reuse previous released bundled sidecar binaries if they are not changed

[Fred-Wu]

Summary

• Reuse unchanged bundled sidecar binaries from the previous GitHub release VSIX during release packaging, skipping Rust setup/build when sidecar inputs have not changed.
• Add release workflow validation to ensure each packaged target contains exactly one expected R_CONSOLE_HOST binary.
• Release workflow now publishes the target-specific VSIX packages to the Open VSX Registry.
• Fix R submission normalization so leading blank lines left behind after stripped full-line comments do not echo before the first real command.
• Bump extension version to 0.2.5.