Implemented Ollama as an embeddings provider

Initial prototype of Ollama embeddings actually working, error handlign / retries still missing.

Allow model to be any String and require dimensions parameter

Fixed rustfmt formatting issues

There were some formatting issues in the initial PR and this should not make the changes comply with the Rust style guidelines

Because I accidentally didn't follow the style guide for commits in my commit messages I squashed them into one to comply

milli/src/vector/error.rs

@@ -2,6 +2,7 @@ use std::path::PathBuf;
 
 use hf_hub::api::sync::ApiError;
 
+use super::ollama::OllamaError;
 use crate::error::FaultSource;
 use crate::vector::openai::OpenAiError;
 
@@ -71,6 +72,15 @@ pub enum EmbedErrorKind {
     OpenAiRuntimeInit(std::io::Error),
     #[error("initializing web client for sending embedding requests failed: {0}")]
     InitWebClient(reqwest::Error),
+    // Dedicated Ollama error kinds, might have to merge them into one cohesive error type for all backends.
+    #[error("unexpected response from Ollama: {0}")]
+    OllamaUnexpected(reqwest::Error),
+    #[error("sent too many requests to Ollama: {0}")]
+    OllamaTooManyRequests(OllamaError),
+    #[error("received internal error from Ollama: {0}")]
+    OllamaInternalServerError(OllamaError),
+    #[error("received unhandled HTTP status code {0} from Ollama")]
+    OllamaUnhandledStatusCode(u16),
 }
 
 impl EmbedError {
@@ -129,6 +139,22 @@ impl EmbedError {
     pub fn openai_initialize_web_client(inner: reqwest::Error) -> Self {
         Self { kind: EmbedErrorKind::InitWebClient(inner), fault: FaultSource::Runtime }
     }
+
+    pub fn ollama_unexpected(inner: reqwest::Error) -> EmbedError {
+        Self { kind: EmbedErrorKind::OllamaUnexpected(inner), fault: FaultSource::Bug }
+    }
+
+    pub(crate) fn ollama_too_many_requests(inner: OllamaError) -> EmbedError {
+        Self { kind: EmbedErrorKind::OllamaTooManyRequests(inner), fault: FaultSource::Runtime }
+    }
+
+    pub(crate) fn ollama_internal_server_error(inner: OllamaError) -> EmbedError {
+        Self { kind: EmbedErrorKind::OllamaInternalServerError(inner), fault: FaultSource::Runtime }
+    }
+
+    pub(crate) fn ollama_unhandled_status_code(code: u16) -> EmbedError {
+        Self { kind: EmbedErrorKind::OllamaUnhandledStatusCode(code), fault: FaultSource::Bug }
+    }
 }
 
 #[derive(Debug, thiserror::Error)]