Claude review: params: Convert generic kernel_param_ops .get helpers to seq_buf

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

Patch Review

This is the core conversion of all standard helpers (`param_get_bool`, `param_get_int`, etc.) and `param_array_get`. Also pulls in lockstep changes to callers that delegate to these helpers (kfence, KVM, dmatest, apparmor).

The `param_array_get` rework is well-done — it now writes directly into the parent `seq_buf` for `.get` ops, only falling back to the bounce buffer for legacy `.get_str` ops.

One thing to note in the `param_array_get` conversion — the replacement of the trailing newline with a comma is done by directly writing to `s->buffer[before - 1]`:

```c
+		if (i && s->buffer[before - 1] == '\n')
+			s->buffer[before - 1] = ',';
```

This is reaching behind `seq_buf`'s back, but it's necessary for the comma-separated output format and mirrors what the old code did with the raw buffer. Acceptable.

**Verdict: Correct conversions. The callers that delegate to standard helpers are properly updated in lockstep.**

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