Fix incorrect code examples in docs for sync/async usage

[Copilot]

Several code examples in docs/API.md and docs/USAGE.md contained correctness bugs — including a C# compile error, calls to non-existent methods, and sync/async API misuse.

docs/USAGE.md

• OpenEntryStreamAsync + WriteEntryToAsync called on same entry — these are mutually exclusive; the implementation throws if both are called. Removed the unused entryStream variable, leaving only WriteEntryToAsync.
• Sync archive opened in async context — ZipArchive.OpenArchive(...) replaced with await ZipArchive.OpenAsyncArchive(...) and foreach replaced with await foreach over EntriesAsync.

docs/API.md

• Duplicate var entry declaration in the same scope (C# compile error) — renamed second declaration to firstEntry.
• Orphaned entry.OpenEntryStreamAsync(...) snippet referenced an undefined entry outside any archive scope — moved into a properly scoped await using async archive block with await foreach over EntriesAsync.
• Async calls inside sync IWriter block — WriteAsync/WriteAllAsync don't exist on IWriter. Removed them from the sync block; added a separate async example using await WriterFactory.OpenAsyncWriter(...) with await using for both stream and writer.
• ZipArchive.Open(...) → ZipArchive.OpenArchive(...) — the former method does not exist.

[Copilot]

Pull request overview

This PR fixes multiple documentation code examples to correctly reflect the library’s sync/async APIs and to remove snippets that would not compile or would call non-existent methods.

Changes:

• Updated docs/USAGE.md examples to avoid mutually exclusive entry APIs and to use async archive open + await foreach over EntriesAsync.
• Updated docs/API.md examples to fix a C# duplicate-variable compile error, properly scope async entry-stream examples, and separate sync vs async writer usage.
• Corrected a docs call site from a non-existent ZipArchive.Open(...) to ZipArchive.OpenArchive(...).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
docs/USAGE.md	Fixes async usage examples to use async archive APIs and removes invalid mixed entry extraction patterns.
docs/API.md	Fixes invalid/mis-scoped examples and corrects method names; separates sync vs async writer examples.

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[Copilot]

In this example block, entry is obtained via FirstOrDefault(...) and can be null, but it’s used unconditionally in entry.OpenEntryStream(). Also, after renaming the later var entry to firstEntry, the “Get entry stream” section now refers back to the potentially-null entry, which makes the sample prone to runtime failure. Consider either (a) changing the lookup to First(...) (or otherwise guaranteeing a non-null entry) or (b) adding a null-check before opening the stream; and ensure the stream example uses the intended variable (firstEntry vs the key-matched entry).