test: add Kover aggregation

[kdroidFilter]

🚀 Description

Wires kotlinx-kover 0.9.8 onto every published library module and adds a large set of tests that drive shipped parsers, fallbacks, and macOS APIs. The aggregated report excludes only generated icon/symbol catalogues (sf-symbols, freedesktop.icons, window.icons). Production packages are not filtered to inflate the number.

On this Mac the published-runtime line coverage is 44.93% (10 873 / 24 198). The 75% koverVerify floor is kept on purpose and will fail check until Linux and Windows native paths are exercised.

📄 Motivation and Context

The published JAR is one coverage denominator across three OS backends. Most of the remaining miss is Tao scene/popup/deco and off-OS JNI, which cannot run here. This PR records the Kover setup and the Mac-reachable / pure-Kotlin work so Linux and Windows can continue on the same branch.

Bugs found while writing tests (fixed in this PR):

• Version.fromString — empty semver groups used toInt() and threw; they now parse as 0 via toIntOrNull() ?: 0.
• FileSelector — the exe format had a suffix mapping (-nsis.) but no .exe extension fallback, so a plain setup.exe was never selected.
• LinuxSystemInfo / WindowsSystemInfo — NativeLibraryLoader caches by library name (nucleus_system_info), so bridge.isLoaded can be true off-platform. ready() now also requires the matching Platform.Current.

🧪 How Has This Been Tested?

From /Users/elie/IdeaProjects/Nucleus-kover-coverage on macOS:

./gradlew :decorated-window-core:test :decorated-window-material3:test \
  :nucleus-application:test :scheduler:test :updater-runtime:test \
  :spellcheck:test :notification-macos:test :darkmode-detector:test \
  :system-color:test :autolaunch:test :core-runtime:test \
  :energy-manager:test :taskbar-progress:test :global-hotkey:test \
  :menu-macos:test :launcher-macos:test :service-management-macos:test \
  --no-configuration-cache
# BUILD SUCCESSFUL

./gradlew :koverXmlReport :koverLog --no-configuration-cache
# application line coverage: 44.9335%

taoHeadfulTest is optional: the Kover agent is attached via an args file, and Robot() cases skip when Accessibility TCC is missing (a hang until the 240s watchdog is treated as a defect).

📦 Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

✅ Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.