chore: bump SDK version to 4.2.0

[TorstenDittmann]

This PR bumps SDK version metadata to 4.2.0 after the concurrent chunk upload update.

[greptile-apps]

Greptile Summary

Bumps the SDK version from 4.1.0 to 4.2.0 across all relevant files, following the concurrent chunk upload feature update.

• Appwrite.csproj: NuGet package version updated to 4.2.0.
• Client.cs: Both the user-agent header string and x-sdk-version header updated to 4.2.0.
• README.md: All three installation code examples updated to reference 4.2.0.

Confidence Score: 5/5

This is a straightforward version string update with no logic changes — safe to merge.

All three files only change version literals from 4.1.0 to 4.2.0, with no behavioural or functional modifications. The changes are consistent across the package metadata, runtime headers, and documentation.

No files require special attention.

Important Files Changed

Filename	Overview
Appwrite/Appwrite.csproj	Version bumped from 4.1.0 to 4.2.0 in the NuGet package metadata
Appwrite/Client.cs	User-Agent string and x-sdk-version header updated from 4.1.0 to 4.2.0
README.md	Installation instructions updated to reference version 4.2.0 in all three code examples

_{Reviews (1): Last reviewed commit: "chore: bump SDK version to 4.2.0" | Re-trigger Greptile}