Follow-up to #14041. Adds a minimal revealjs presentation fixture
and includes it as Test 3 in the manual testing protocol, covering
reveal.js asset bundling verification.

Confirmed working: `quarto publish posit-connect-cloud` successfully
publishes revealjs slides with all assets intact.

The Install SMCTL step had no error handling: a failed S3 download
(0 bytes) led to a silent msiexec failure, but the script
unconditionally declared success and added the path to GITHUB_PATH.

Add download retry with file size validation, synchronous msiexec
via Start-Process -Wait, and post-install binary verification.

* Support tar.xz and self-extracting exe in unzip()

Change `tar xfz` to `tar xf` for automatic compression detection,
handling .tar.gz, .tgz, and .tar.xz files. Add .exe branch for
self-extracting 7z archives used by TinyTeX's new Windows naming.

* Add unit tests for TinyTeX package name generation

Pure logic tests for all platform/arch combos via options parameter.
Asset-existence tests verify candidates match actual release assets,
catching naming drift in CI.

* Support ARM64 Linux and adopt new TinyTeX naming scheme

Remove the needsSourceInstall() prereq gate that blocks ARM64 Linux.
Update tinyTexPkgName() to generate candidate filenames for both new
(TinyTeX-{os}[-{arch}]-{ver}.{ext}) and old naming schemes, with new
preferred and old as fallback. Update tinyTexUrl() to pick the first
matching asset from release. Handles the transition seamlessly as
releases adopt new naming.

Fixes #12124

* Add changelog entry for ARM64 Linux TinyTeX support

* Guard .exe extraction to Windows and improve error diagnostics

Only attempt self-extracting .exe on Windows in unzip().
Include candidate filenames in TinyTeX download error for easier
debugging when naming drift occurs.