This fixes two issues with the terminal tests that caused failures on Windows runners:
1. Replaced hardcoded '/' with path.join() for R_PROFILE_USER check.
2. Stubbed util.getRterm to resolve to process.execPath instead of 'R' to ensure the path exists when checked by fs.existsSync().

…lity

Squashed commits for session integration tests, CI workflow updates, and lint fixes.

…assertions

Rename `r-ipc-vscode.test.ts` to `session.test.ts` to match naming conventions. Explicitly assert webview panel creation for `svglite` and `png` plots by mocking `globalPlotManager` to ensure the plot viewer correctly responds to events.

…errors

- Remove .External.graphics rebinding which caused state conflicts.
- Use pdf(NULL) and sess.null_dev option for stable background plot capture.
- Ensure plot rendering doesn't accidentally close the user's primary device.
- Add grDevices:: prefixes for more robust name resolution.

- Replaced httpuv/WebSockets with nanonext/NNG in 'sess' R package.
- Updated VS Code extension to use net.Socket for IPC.
- Implemented length-prefixed message framing.
- Fixed Windows IPC path compatibility.
- Incremented sess package version to 0.1.1 to force reinstallation.
- Note: R server side currently uses non-existent 'stream_aio' and needs further fixes.