Add CodexHttpClient wrapper with request logging (#5564)

## Summary
- wrap the default reqwest::Client inside a new
CodexHttpClient/CodexRequestBuilder pair and log the HTTP method, URL,
and status for each request
- update the auth/model/provider plumbing to use the new builder helpers
so headers and bearer auth continue to be applied consistently
- add the shared `http` dependency that backs the header conversion
helpers

## Testing
- `CODEX_SANDBOX=seatbelt CODEX_SANDBOX_NETWORK_DISABLED=1 cargo test -p
codex-core`
- `CODEX_SANDBOX=seatbelt CODEX_SANDBOX_NETWORK_DISABLED=1 cargo test -p
codex-chatgpt`
- `CODEX_SANDBOX=seatbelt CODEX_SANDBOX_NETWORK_DISABLED=1 cargo test -p
codex-tui`

------
https://chatgpt.com/codex/tasks/task_i_68fa5038c17483208b1148661c5873be

codex-rs/core/src/model_provider_info.rs

@@ -6,6 +6,8 @@
 //!      key. These override or extend the defaults at runtime.
 
 use crate::CodexAuth;
+use crate::default_client::CodexHttpClient;
+use crate::default_client::CodexRequestBuilder;
 use codex_app_server_protocol::AuthMode;
 use serde::Deserialize;
 use serde::Serialize;
@@ -95,7 +97,7 @@ pub struct ModelProviderInfo {
 
 impl ModelProviderInfo {
     /// Construct a `POST` RequestBuilder for the given URL using the provided
-    /// reqwest Client applying:
+    /// [`CodexHttpClient`] applying:
     ///   • provider-specific headers (static + env based)
     ///   • Bearer auth header when an API key is available.
     ///   • Auth token for OAuth.
@@ -104,9 +106,9 @@ impl ModelProviderInfo {
     /// one produced by [`ModelProviderInfo::api_key`].
     pub async fn create_request_builder<'a>(
         &'a self,
-        client: &'a reqwest::Client,
+        client: &'a CodexHttpClient,
         auth: &Option<CodexAuth>,
-    ) -> crate::error::Result<reqwest::RequestBuilder> {
+    ) -> crate::error::Result<CodexRequestBuilder> {
         let effective_auth = if let Some(secret_key) = &self.experimental_bearer_token {
             Some(CodexAuth::from_api_key(secret_key))
         } else {
@@ -187,9 +189,9 @@ impl ModelProviderInfo {
     }
 
     /// Apply provider-specific HTTP headers (both static and environment-based)
-    /// onto an existing `reqwest::RequestBuilder` and return the updated
+    /// onto an existing [`CodexRequestBuilder`] and return the updated
     /// builder.
-    fn apply_http_headers(&self, mut builder: reqwest::RequestBuilder) -> reqwest::RequestBuilder {
+    fn apply_http_headers(&self, mut builder: CodexRequestBuilder) -> CodexRequestBuilder {
         if let Some(extra) = &self.http_headers {
             for (k, v) in extra {
                 builder = builder.header(k, v);