Widen Process arguments to IEnumerable<string>

[SimonCropp]

Run, RunAsync, RunAndCaptureText, RunAndCaptureTextAsync and StartAndForget declare arguments as IList<string>?, but net11 RC1 ships them as IEnumerable<string>?:

ProcessExitStatus Run(string fileName, IEnumerable<string>? arguments = null, bool silent = false, TimeSpan? timeout = null)

So passing a sequence that is not a list — a LINQ result, an IReadOnlyList<string>, a HashSet<string> — compiles on net11 and fails to compile on every polyfilled target framework. That is the break the package exists to prevent.

The signatures came from #547, written against an earlier preview where the parameter was IList<string>. The shape changed before RC1.

Widening is source compatible for existing callers.

Changes

• The five public methods, plus the RunSilentAsync and BuildStartInfo helpers that carried the type through. BuildStartInfo only enumerated the arguments, so no bodies changed.
• The five //Link: overload anchors, which encode the parameter type (system-collections-generic-ilist((system-string)) to ...-ienumerable((system-string))). They would otherwise point at an overload that does not exist.
• Consume.cs now calls all five through a variable typed IEnumerable<string> backed by a HashSet<string>, so a non-list sequence has to bind. That is a compile check across all 22 target frameworks, and on net11 it compiles against the BCL, so both sides are pinned.

API count is unchanged at 1038, since this is a signature change rather than a new API.

Verification

• Solution builds clean in Release, Consume rebuilds clean in Debug across all 22 target frameworks.
• Tests green on net11.0 (1601), net462 (1581) and net8.0 (1598).
• ApiBuilderTests rerun to regenerate the Split files, api_list.include.md and the readme.