LeaveOpen wasn't respected by GZip

[adamhathcock]

bugfix from: #1282

This pull request makes a small change to the GZipStream class to ensure that the LeaveStreamOpen option from readerOptions is passed when initializing the stream. This helps control whether the underlying stream remains open after the GZipStream is disposed.

[Copilot]

Pull request overview

This PR aims to ensure IReaderOptions.LeaveStreamOpen is honored when constructing the internal GZip stream so callers can control whether the underlying stream is disposed.

Changes:

• Pass readerOptions.LeaveStreamOpen into the GZipStream initialization call.

Issue found (blocks approval):

• The new argument uses readerOptions.LeaveStreamOpen before the existing null-guard (readerOptions ?? throw ...) used in the subsequent argument. If readerOptions is ever null (which the guard implies is possible/expected), this now throws NullReferenceException earlier. The fix is to read LeaveStreamOpen from the same null-checked expression (or assign a local after the guard).