Bumping .NET version

Adds support for additional arguments in TailwindHostedService

The test project pulled System.Net.Http 4.3.0 and System.Text.RegularExpressions
4.3.0 (both High severity advisories) through old xunit and FakeItEasy versions.
Moves the test project to net8.0 with current test packages, and updates CI to
the .NET 8 SDK and actions/checkout@v4. The published library still targets net6.0.

The CLI lookup used to try every executable on PATH whose name contained
"tailwind", plus matching files in the current directory, which could run an
unrelated or planted binary. A configured TailwindCliPath is now used as given;
the default falls back only to tailwindcss and the standalone binary's
published name for the platform, resolved from PATH by the OS.

…-1-fea0

Clear vulnerable transitive packages in test project; update CI

net6.0 no longer receives security patches. The library now multi-targets
net8.0 and net10.0, referencing SpaServices.Extensions 8.0.33 and 10.0.14
respectively, and the tests run on both. Replaces the deprecated
PackageLicenseUrl with PackageLicenseExpression MIT.

Only run the configured or well-known Tailwind CLI

Target net8.0 and net10.0 instead of end-of-life net6.0

The release workflow now gets a short-lived nuget.org API key through
NuGet/login (GitHub OIDC) rather than the long-lived NUGET_API_KEY secret.
Also gives the workflow a name, fixes its indentation, and uploads the
build artifacts before pushing so they're kept if the push fails.

…lishing

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