feat(csharp): implement delete_segments method (#2626)

[atharvalade]

Add IIggySegment interface, TCP/HTTP client support, and integration tests for the delete_segments API method.

Which issue does this PR close?

Closes #2626

Rationale

The C# SDK was missing the delete_segments API method. This brings it in line with the Rust client architecture which has a separate SegmentClient trait.

What changed?

The C# SDK had no way to delete segments from a partition. The Rust SDK exposes this via a dedicated SegmentClient trait with binary (TCP command code 503) and HTTP (DELETE .../partitions/{pid}?segments_count=N) support.

Added a new IIggySegment interface with DeleteSegmentsAsync, implemented it in both TcpMessageStream and HttpMessageStream, wired it into IIggyClient, and added integration tests (TCP only — the server doesn't expose an HTTP segments endpoint yet).

Local Execution

• Passed, SDK, unit tests (85/85), and integration test project all build with 0 warnings/errors
• Pre-commit hooks ran, trailing whitespace, trailing newline, mixed line endings, dotnet format all passed. License headers check skipped (addlicense/Go not installed locally, but headers verified manually against existing files).

AI Usage

1. Opus 4.6
2. Auditing binary format byte-by-byte against Rust
3. Built all projects (0 warnings/errors), ran 85 unit tests (all passed), verified binary wire format and HTTP query params match Rust SDK exactly, ran pre-commit hooks
4. Yes