[bazel] Improve runfiles handling (#10098)

we can't use runfiles directory on Windows due to path lengths, so swap
to manifest strategy. Parsing the manifest is a bit complex and the
format is changing in Bazel upstream, so pull in the official Rust
library (via a small hack to make it importable...) and cleanup all the
associated logic to work cleanly in both bazel and cargo without extra
confusion

codex-rs/utils/cargo-bin/README.md

@@ -0,0 +1,20 @@
+# codex-utils-cargo-bin runfiles strategy
+
+We disable the directory-based runfiles strategy and rely on the manifest
+strategy across all platforms. This avoids Windows path length issues and keeps
+behavior consistent in local and remote builds on all platforms. Bazel sets
+`RUNFILES_MANIFEST_FILE`, and the `codex-utils-cargo-bin` helpers use the
+`runfiles` crate to resolve runfiles via that manifest.
+
+Function behavior:
+- `cargo_bin`: reads `CARGO_BIN_EXE_*` environment variables (set by Cargo or
+  Bazel) and resolves them via the runfiles manifest when `RUNFILES_MANIFEST_FILE`
+  is present. When not under runfiles, it only accepts absolute paths from
+  `CARGO_BIN_EXE_*` and returns an error otherwise.
+- `find_resource!`: used by tests to locate fixtures. It chooses the Bazel
+  runfiles resolution path when `RUNFILES_MANIFEST_FILE` is set, otherwise it
+  falls back to a `CARGO_MANIFEST_DIR`-relative path for Cargo runs.
+
+Background:
+- https://bazel.build/docs/runfiles
+- https://bazel.build/docs/runfiles#runfiles-manifest