assistant: Overhaul provider infrastructure (#14929)

<img width="624" alt="image"
src="https://github.com/user-attachments/assets/f492b0bd-14c3-49e2-b2ff-dc78e52b0815">

- [x] Correctly set custom model token count
- [x] How to count tokens for Gemini models?
- [x] Feature flag zed.dev provider
- [x] Figure out how to configure custom models
- [ ] Update docs

Release Notes:

- Added support for quickly switching between multiple language model
providers in the assistant panel

---------

Co-authored-by: Antonio <antonio@zed.dev>

crates/language_model/src/settings.rs

@@ -0,0 +1,143 @@
+use std::time::Duration;
+
+use anyhow::Result;
+use gpui::AppContext;
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+use settings::{Settings, SettingsSources};
+
+use crate::{
+    provider::{
+        anthropic::AnthropicSettings, cloud::ZedDotDevSettings, ollama::OllamaSettings,
+        open_ai::OpenAiSettings,
+    },
+    CloudModel,
+};
+
+/// Initializes the language model settings.
+pub fn init(cx: &mut AppContext) {
+    AllLanguageModelSettings::register(cx);
+}
+
+#[derive(Default)]
+pub struct AllLanguageModelSettings {
+    pub open_ai: OpenAiSettings,
+    pub anthropic: AnthropicSettings,
+    pub ollama: OllamaSettings,
+    pub zed_dot_dev: ZedDotDevSettings,
+}
+
+#[derive(Default, Clone, Debug, Serialize, Deserialize, PartialEq, JsonSchema)]
+pub struct AllLanguageModelSettingsContent {
+    pub anthropic: Option<AnthropicSettingsContent>,
+    pub ollama: Option<OllamaSettingsContent>,
+    pub open_ai: Option<OpenAiSettingsContent>,
+    #[serde(rename = "zed.dev")]
+    pub zed_dot_dev: Option<ZedDotDevSettingsContent>,
+}
+
+#[derive(Default, Clone, Debug, Serialize, Deserialize, PartialEq, JsonSchema)]
+pub struct AnthropicSettingsContent {
+    pub api_url: Option<String>,
+    pub low_speed_timeout_in_seconds: Option<u64>,
+    pub available_models: Option<Vec<anthropic::Model>>,
+}
+
+#[derive(Default, Clone, Debug, Serialize, Deserialize, PartialEq, JsonSchema)]
+pub struct OllamaSettingsContent {
+    pub api_url: Option<String>,
+    pub low_speed_timeout_in_seconds: Option<u64>,
+}
+
+#[derive(Default, Clone, Debug, Serialize, Deserialize, PartialEq, JsonSchema)]
+pub struct OpenAiSettingsContent {
+    pub api_url: Option<String>,
+    pub low_speed_timeout_in_seconds: Option<u64>,
+    pub available_models: Option<Vec<open_ai::Model>>,
+}
+
+#[derive(Default, Clone, Debug, Serialize, Deserialize, PartialEq, JsonSchema)]
+pub struct ZedDotDevSettingsContent {
+    available_models: Option<Vec<CloudModel>>,
+}
+
+impl settings::Settings for AllLanguageModelSettings {
+    const KEY: Option<&'static str> = Some("language_models");
+
+    type FileContent = AllLanguageModelSettingsContent;
+
+    fn load(sources: SettingsSources<Self::FileContent>, _: &mut AppContext) -> Result<Self> {
+        fn merge<T>(target: &mut T, value: Option<T>) {
+            if let Some(value) = value {
+                *target = value;
+            }
+        }
+
+        let mut settings = AllLanguageModelSettings::default();
+
+        for value in sources.defaults_and_customizations() {
+            merge(
+                &mut settings.anthropic.api_url,
+                value.anthropic.as_ref().and_then(|s| s.api_url.clone()),
+            );
+            if let Some(low_speed_timeout_in_seconds) = value
+                .anthropic
+                .as_ref()
+                .and_then(|s| s.low_speed_timeout_in_seconds)
+            {
+                settings.anthropic.low_speed_timeout =
+                    Some(Duration::from_secs(low_speed_timeout_in_seconds));
+            }
+            merge(
+                &mut settings.anthropic.available_models,
+                value
+                    .anthropic
+                    .as_ref()
+                    .and_then(|s| s.available_models.clone()),
+            );
+
+            merge(
+                &mut settings.ollama.api_url,
+                value.ollama.as_ref().and_then(|s| s.api_url.clone()),
+            );
+            if let Some(low_speed_timeout_in_seconds) = value
+                .ollama
+                .as_ref()
+                .and_then(|s| s.low_speed_timeout_in_seconds)
+            {
+                settings.ollama.low_speed_timeout =
+                    Some(Duration::from_secs(low_speed_timeout_in_seconds));
+            }
+
+            merge(
+                &mut settings.open_ai.api_url,
+                value.open_ai.as_ref().and_then(|s| s.api_url.clone()),
+            );
+            if let Some(low_speed_timeout_in_seconds) = value
+                .open_ai
+                .as_ref()
+                .and_then(|s| s.low_speed_timeout_in_seconds)
+            {
+                settings.open_ai.low_speed_timeout =
+                    Some(Duration::from_secs(low_speed_timeout_in_seconds));
+            }
+            merge(
+                &mut settings.open_ai.available_models,
+                value
+                    .open_ai
+                    .as_ref()
+                    .and_then(|s| s.available_models.clone()),
+            );
+
+            merge(
+                &mut settings.zed_dot_dev.available_models,
+                value
+                    .zed_dot_dev
+                    .as_ref()
+                    .and_then(|s| s.available_models.clone()),
+            );
+        }
+
+        Ok(settings)
+    }
+}