Add XML docs to all publicly exposed extensions

[Copilot]

Adds /// <summary> XML documentation to every public method and property across all extension files and Disposable.

• EnumerableExtensions — ToSingletonEnumerable, WhereNotNull (reference + value type), WhereNotNullOrEmpty, WhereNotNullOrWhiteSpace, FirstOrNull, LastOrNull, ElementAtOrNull
• AsyncEnumerableExtensions — TakeAsync, SelectManyAsync, ToListAsync, GetAwaiter
• ComparableExtensions — Clamp, Min, Max
• ExceptionExtensions — GetSelfAndDescendants
• FunctionalExtensions — Pipe, NullIf, NullIfDefault, NullIfEmpty, NullIfWhiteSpace
• PathExtensions — GetInvalidFileNameChars, GetInvalidPathChars, EscapeFileName
• StreamExtensions — three CopyToAsync overloads
• StringExtensions — SubstringUntil, SubstringUntilLast, SubstringAfter, SubstringAfterLast, Truncate, SeparateWords, ToKebabCase, ToSnakeCase
• StringBuilderExtensions — AppendIfNotEmpty, Trim
• TextReaderExtensions — ReadLinesAsync
• AggregateExceptionExtensions — TryGetSingle
• Disposable — class-level summary, Dispose, Null, Create, Merge

[Tyrrrz]

@copilot

[Tyrrrz]

Suggested change

	/// Projects each element of the async sequence to an <see cref="IEnumerable{T}"/>
	/// Projects each element of the async sequence to an <see cref="IEnumerable{T}" />

Always leave a space before />

[Copilot]

Fixed in 9e94ffc — added a space before /> in all self-closing XML doc tags across all files.

[Copilot]

Pull request overview

This PR adds XML <summary> documentation (and a few <inheritdoc /> usages) to extension methods and the Disposable utility to improve IntelliSense and generated API docs consistency across PowerKit.

Changes:

• Added <summary> XML docs to extension methods across the PowerKit.Extensions set.
• Added class/member XML docs to Disposable, including docs for Null, Create, and Merge.
• Standardized brief behavioral descriptions for string/stream/path/sequence helpers.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
PowerKit/Extensions/TextReaderExtensions.cs	Adds XML summary for ReadLinesAsync.
PowerKit/Extensions/StringExtensions.cs	Adds XML summaries for substring helpers, truncation, word separation, and casing helpers.
PowerKit/Extensions/StringBuilderExtensions.cs	Adds XML summaries for AppendIfNotEmpty and Trim.
PowerKit/Extensions/StreamExtensions.cs	Adds XML summaries for CopyToAsync overloads (autoflush/progress variants).
PowerKit/Extensions/PathExtensions.cs	Adds XML summaries for invalid char helpers and EscapeFileName.
PowerKit/Extensions/FunctionalExtensions.cs	Adds XML summaries for Pipe and NullIf* helpers.
PowerKit/Extensions/ExceptionExtensions.cs	Adds XML summary for GetSelfAndDescendants.
PowerKit/Extensions/EnumerableExtensions.cs	Adds XML summaries for singleton wrapping, filtering, and *OrNull helpers.
PowerKit/Extensions/ComparableExtensions.cs	Adds XML summaries for Clamp, Min, Max.
PowerKit/Extensions/AsyncEnumerableExtensions.cs	Adds XML summaries for async sequence helpers (TakeAsync, SelectManyAsync, ToListAsync, GetAwaiter).
PowerKit/Extensions/AggregateExceptionExtensions.cs	Adds XML summary for TryGetSingle.
PowerKit/Disposable.cs	Adds XML docs for the type and core factory/composition members.

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