fix(test): [T176] make display goldens CRLF-tolerant on Windows (#275)

With the content fixes in, the v0.6.6 CI went green on every Linux and macOS Julia
job (lts/1.10/1); only Julia LTS on windows-latest failed — and purely on line
endings. Git's autocrlf checks the golden `.txt` files out with CRLF on Windows, so
`read(path)` returns `\r\n`-terminated lines while the canonicalized render is LF,
making all 19 goldens mismatch on a trailing `\r`.

Two-part fix (no golden content change, no regeneration):
- `.gitattributes`: pin `test/display/goldens/*.txt` to `eol=lf` so Git never
  rewrites them to CRLF on checkout (root cause).
- `_check_golden`: normalize `\r\n`/`\r` → `\n` when reading the golden, as
  defense-in-depth for any stray CRLF checkout regardless of Git config.

Verified locally: for all 19 fixtures, a simulated CRLF golden and an LF golden both
compare equal to the LF canonical render.

Claude-Session: https://claude.ai/code/session_01QZizX88NDsBZrBgdqPcLQp
