fix(health): check hererocks' luarocks.bat on Windows

[cstrahan]

Description

On Windows, hererocks installs lazy-rocks/hererocks/bin/luarocks.bat. M.build() already spawns it with the .bat extension (rockspec.lua, if Util.is_win then luarocks = luarocks .. ".bat" end), but the health check (M.check()) passes M.hererocks.bin("luarocks") without it. vim.fn.executable() accepts the extensionless path (PATHEXT), but spawning it fails, so :checkhealth lazy reports a working install as broken:

- ❌ ERROR failed to get version of {C:/Users/.../nvim-data/lazy-rocks/hererocks/bin/luarocks}
  Failed to spawn process C:/Users/.../nvim-data/lazy-rocks/hererocks/bin/luarocks {
- ❌ ERROR {C:/Users/.../nvim-data/lazy-rocks/hererocks/bin/luarocks} not installed
- ⚠️ WARNING Lazy won't be able to install plugins that require `luarocks`.

This uses luarocks.bat on Windows in the health check too.

Tested on Windows 10 with Neovim 0.12.5 and a hererocks install (Lua 5.1.5, LuaRocks 3.8.0):

• require("lazy.manage.process").exec({ ".../bin/luarocks", "--version" }) fails to spawn; with .../bin/luarocks.bat it returns exit code 0 and LuaRocks' version;
• :checkhealth lazy before: 2 errors and the warning above; after: ✅ OK {.../bin/luarocks.bat} ... 3.8.0 and no luarocks errors or warnings.

Related Issue(s)

None that I found.

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