Use anyhow more idiomatically (#31052)

https://github.com/zed-industries/zed/issues/30972 brought up another
case where our context is not enough to track the actual source of the
issue: we get a general top-level error without inner error.

The reason for this was `.ok_or_else(|| anyhow!("failed to read HEAD
SHA"))?; ` on the top level.

The PR finally reworks the way we use anyhow to reduce such issues (or
at least make it simpler to bubble them up later in a fix).
On top of that, uses a few more anyhow methods for better readability.

* `.ok_or_else(|| anyhow!("..."))`, `map_err` and other similar error
conversion/option reporting cases are replaced with `context` and
`with_context` calls
* in addition to that, various `anyhow!("failed to do ...")` are
stripped with `.context("Doing ...")` messages instead to remove the
parasitic `failed to` text
* `anyhow::ensure!` is used instead of `if ... { return Err(...); }`
calls
* `anyhow::bail!` is used instead of `return Err(anyhow!(...));`

Release Notes:

- N/A

crates/project/src/context_server_store.rs

@@ -233,9 +233,10 @@ impl ContextServerStore {
     }
 
     pub fn stop_server(&mut self, id: &ContextServerId, cx: &mut Context<Self>) -> Result<()> {
-        let Some(state) = self.servers.remove(id) else {
-            return Err(anyhow::anyhow!("Context server not found"));
-        };
+        let state = self
+            .servers
+            .remove(id)
+            .context("Context server not found")?;
 
         let server = state.server();
         let configuration = state.configuration();
@@ -336,9 +337,10 @@ impl ContextServerStore {
     }
 
     fn remove_server(&mut self, id: &ContextServerId, cx: &mut Context<Self>) -> Result<()> {
-        let Some(state) = self.servers.remove(id) else {
-            return Err(anyhow::anyhow!("Context server not found"));
-        };
+        let state = self
+            .servers
+            .remove(id)
+            .context("Context server not found")?;
         drop(state);
         cx.emit(Event::ServerStatusChanged {
             server_id: id.clone(),
@@ -1097,7 +1099,7 @@ mod tests {
 
                         self.tx
                             .unbounded_send(response.to_string())
-                            .map_err(|e| anyhow::anyhow!("Failed to send message: {}", e))?;
+                            .context("sending a message")?;
                     }
                 }
             }