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/dap_adapters/src/python.rs

@@ -1,4 +1,5 @@
 use crate::*;
+use anyhow::Context as _;
 use dap::{DebugRequest, StartDebuggingRequestArguments, adapters::DebugTaskDefinition};
 use gpui::{AsyncApp, SharedString};
 use language::LanguageName;
@@ -112,7 +113,7 @@ impl PythonDebugAdapter {
                 file_name.starts_with(&file_name_prefix)
             })
             .await
-            .ok_or_else(|| anyhow!("Debugpy directory not found"))?
+            .context("Debugpy directory not found")?
         };
 
         let toolchain = delegate
@@ -143,7 +144,7 @@ impl PythonDebugAdapter {
         };
 
         Ok(DebugAdapterBinary {
-            command: python_path.ok_or(anyhow!("failed to find binary path for python"))?,
+            command: python_path.context("failed to find binary path for Python")?,
             arguments: vec![
                 debugpy_dir
                     .join(Self::ADAPTER_PATH)