Fix GitHub token auto discovery (#1335)

* Fix GitHub token auto discovery

Fixed #1333

 - Rm dep `gh-token` since it is broken and we can simply run
   `gh auth token` in `cargo-binstall` instead.
 - binstalk-downloader: Make sure GitHub token is at least 40B long
   and other than the `_`, composes of only alphanumeric characters.
 - Warn on failure to read `git/credential` files
 - Optimize `try_from_home` to avoid heap allocation of `PathBuf`

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

* Fix typo and clippy

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

* Simplify `is_valid_gh_token` & `is_ascii_alphanumeric` impl

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

* Improve err msg in `get_inner`

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

* Improve err msg of `cargo_binstall::gh_token::get`

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

---------

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

crates/bin/src/gh_token.rs

@@ -0,0 +1,38 @@
+use std::{io, process};
+
+use compact_str::CompactString;
+use tracing::warn;
+
+fn get_inner() -> io::Result<CompactString> {
+    let process::Output { status, stdout, .. } = process::Command::new("gh")
+        .args(["auth", "token"])
+        .stdin(process::Stdio::null())
+        .stdout(process::Stdio::piped())
+        .stderr(process::Stdio::null())
+        .output()?;
+
+    if !status.success() {
+        return Err(io::Error::new(
+            io::ErrorKind::Other,
+            format!("process exited with `{status}`"),
+        ));
+    }
+
+    // Use String here instead of CompactString here since
+    // `CompactString::from_utf8` allocates if it's longer than 24B.
+    let s = String::from_utf8(stdout).map_err(|_err| {
+        io::Error::new(io::ErrorKind::InvalidData, "Invalid output, expected utf8")
+    })?;
+
+    Ok(s.trim().into())
+}
+
+pub(super) fn get() -> Option<CompactString> {
+    match get_inner() {
+        Ok(token) => Some(token),
+        Err(err) => {
+            warn!(?err, "Failed to retrieve token from `gh auth token`");
+            None
+        }
+    }
+}