Add kernel-session cancellation via --session-id

## Problem

`kaggle kernels` has no command for stopping an accidentally submitted run. The public API already exposes `ApiCancelKernelSessionRequest`, but the public CLI does not expose it.

## Reproduction and API boundary

With `kaggle==2.2.4`, `kaggle kernels --help` exposes no cancellation command.

I also validated the existing status endpoint against a real private CPU kernel while it was `RUNNING`: its raw response contains `status` and `failureMessage`, but no `kernelSessionId`. `GetKernel` likewise exposes metadata and source but no current session identity. Therefore closed PR #967 cannot reliably implement a kernel-reference form by extracting an ID from the public status response.

The Kaggle editor has a separate internal API that returns run IDs, but the CLI should not depend on that undocumented web API.

## Requested behavior

Add the small supported public-API wrapper:

```bash
kaggle kernels cancel --session-id SESSION_ID
```

It should invoke the existing cancel-session endpoint, surface its error message, and not delete the kernel, inputs, or historical outputs.

A future `kaggle kernels cancel OWNER/KERNEL-SLUG` needs a public API contract that resolves a kernel reference to a cancellable session ID; that is intentionally out of scope here.

## Proposed contribution

I will submit a focused CLI command with parser and API-wrapper tests. The implementation will use only the supported generated SDK request, not raw web requests.

The entry point is `kaggle kernels cancel --session-id SESSION_ID`; start by locating the existing generated `ApiCancelKernelSessionRequest` usage and the kernels command parser. Add parser and API-wrapper tests for cancellation, error propagation, and preserving kernel data; done means the command uses the supported SDK API without relying on the undocumented web API.

Written by the indexing model from the issue text.