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/proto/src/error.rs

@@ -124,7 +124,7 @@ impl ErrorExt for anyhow::Error {
         if let Some(rpc_error) = self.downcast_ref::<RpcError>() {
             rpc_error.cloned()
         } else {
-            anyhow::anyhow!("{}", self)
+            anyhow::anyhow!("{self}")
         }
     }
 }

crates/proto/src/typed_envelope.rs

@@ -1,5 +1,5 @@
 use crate::{Envelope, PeerId};
-use anyhow::{Result, anyhow};
+use anyhow::{Context as _, Result};
 use serde::Serialize;
 use std::{
     any::{Any, TypeId},
@@ -201,7 +201,7 @@ pub struct TypedEnvelope<T> {
 impl<T> TypedEnvelope<T> {
     pub fn original_sender_id(&self) -> Result<PeerId> {
         self.original_sender_id
-            .ok_or_else(|| anyhow!("missing original_sender_id"))
+            .context("missing original_sender_id")
     }
 }