feat: make reasoning effort/summaries configurable (#1199)

Previous to this PR, we always set `reasoning` when making a request
using the Responses API:


https://github.com/openai/codex/blob/d7245cbbc9d8ff5446da45e5951761103492476d/codex-rs/core/src/client.rs#L108-L111

Though if you tried to use the Rust CLI with `--model gpt-4.1`, this
would fail with:

```shell
"Unsupported parameter: 'reasoning.effort' is not supported with this model."
```

We take a cue from the TypeScript CLI, which does a check on the model
name:


https://github.com/openai/codex/blob/d7245cbbc9d8ff5446da45e5951761103492476d/codex-cli/src/utils/agent/agent-loop.ts#L786-L789

This PR does a similar check, though also adds support for the following
config options:

```
model_reasoning_effort = "low" | "medium" | "high" | "none"
model_reasoning_summary = "auto" | "concise" | "detailed" | "none"
```

This way, if you have a model whose name happens to start with `"o"` (or
`"codex"`?), you can set these to `"none"` to explicitly disable
reasoning, if necessary. (That said, it seems unlikely anyone would use
the Responses API with non-OpenAI models, but we provide an escape
hatch, anyway.)

This PR also updates both the TUI and `codex exec` to show `reasoning
effort` and `reasoning summaries` in the header.

codex-rs/core/src/lib.rs

@@ -34,3 +34,5 @@ mod rollout;
 mod safety;
 mod user_notification;
 pub mod util;
+
+pub use client_common::model_supports_reasoning_summaries;