LM Studio OSS Support (#2312)

## Overview

Adds LM Studio OSS support. Closes #1883


### Changes
This PR enhances the behavior of `--oss` flag to support LM Studio as a
provider. Additionally, it introduces a new flag`--local-provider` which
can take in `lmstudio` or `ollama` as values if the user wants to
explicitly choose which one to use.

If no provider is specified `codex --oss` will auto-select the provider
based on whichever is running.

#### Additional enhancements 
The default can be set using `oss-provider` in config like:

```
oss_provider = "lmstudio"
```

For non-interactive users, they will need to either provide the provider
as an arg or have it in their `config.toml`

### Notes
For best performance, [set the default context
length](https://lmstudio.ai/docs/app/advanced/per-model) for gpt-oss to
the maximum your machine can support

---------

Co-authored-by: Matt Clayton <matt@lmstudio.ai>
Co-authored-by: Eric Traut <etraut@openai.com>

codex-rs/Cargo.lock

@@ -1061,6 +1061,8 @@ dependencies = [
  "clap",
  "codex-app-server-protocol",
  "codex-core",
+ "codex-lmstudio",
+ "codex-ollama",
  "codex-protocol",
  "once_cell",
  "serde",
@@ -1159,7 +1161,6 @@ dependencies = [
  "codex-arg0",
  "codex-common",
  "codex-core",
- "codex-ollama",
  "codex-protocol",
  "core_test_support",
  "libc",
@@ -1278,6 +1279,19 @@ dependencies = [
  "tokio",
 ]
 
+[[package]]
+name = "codex-lmstudio"
+version = "0.0.0"
+dependencies = [
+ "codex-core",
+ "reqwest",
+ "serde_json",
+ "tokio",
+ "tracing",
+ "which",
+ "wiremock",
+]
+
 [[package]]
 name = "codex-login"
 version = "0.0.0"
@@ -1475,7 +1489,6 @@ dependencies = [
  "codex-feedback",
  "codex-file-search",
  "codex-login",
- "codex-ollama",
  "codex-protocol",
  "codex-windows-sandbox",
  "color-eyre",
@@ -1498,6 +1511,7 @@ dependencies = [
  "ratatui",
  "ratatui-macros",
  "regex-lite",
+ "reqwest",
  "serde",
  "serde_json",
  "serial_test",