Claude review: gpu: nova-core: gsp: add tests for SplitState

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

Adds kunit tests with a `TestPayload` helper (using `Command = ()` and `MsgFunction::Nop`). The `check_split` function verifies both the number of continuation records and that concatenating all payloads reproduces the original data.

The boundary conditions tested are:

| `payload_size` | Expected continuations | Reason |
|---|---|---|
| 0 | 0 | Empty payload, no split |
| `MAX_CMD_SIZE` | 0 | Exactly fits single element |
| `MAX_CMD_SIZE + 1` | 1 | Overflows by 1 byte |
| `MAX_CMD_SIZE * 2` | 1 | Two full chunks |
| `MAX_CMD_SIZE * 2 + 1` | 2 | Two full + 1 byte overflow |
| `MAX_CMD_SIZE * 3.5` | 3 | Partial last chunk |

Good coverage of the boundary conditions. The data integrity check (`assert_eq!(buf.as_slice(), ...)`) validates both splitting and reassembly.

**Observation**: Since `TestPayload` uses `Command = ()`, `MAX_FIRST_PAYLOAD_SIZE == MAX_CMD_SIZE`. A test with a non-zero-sized `Command` type would also exercise the case where the first chunk has less variable payload space than continuation chunks. This is a minor gap — the logic is straightforward (`MAX_FIRST_PAYLOAD_SIZE = MAX_CMD_SIZE - size_of::<Command>()`), but a test would provide extra confidence.

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Generated by Claude Code Patch Reviewer