Nested Cargo detection reports only one root when a repo has several disjoint crate directories

[andrew]

#139 finds a nested Cargo.toml when there is no root one, but stops after the first. A repo with several independent crate roots (not workspace members of each other) reports only one in manifests[], so the bridge tools and dependencies from the others are missed.

$ brief --json https://github.com/huggingface/tokenizers | jq '[.manifests[]|select(.ecosystem=="cargo")|.path]'
["tokenizers/Cargo.toml"]
$ git -C tokenizers ls-files -- '**/Cargo.toml'
bindings/node/Cargo.toml
bindings/python/Cargo.toml
bindings/python/tools/stub-gen/Cargo.toml
tokenizers/Cargo.toml

bindings/python/Cargo.toml has pyo3 and bindings/node/Cargo.toml has napi, so tools.native_extension stays empty and dependencies[] misses both.

Repos where git ls-files -- '**/Cargo.toml' finds a root that is not under any directory brief listed:

repo	brief found	git ls-files also finds
https://github.com/huggingface/tokenizers	tokenizers/	bindings/python/ (pyo3), bindings/node/ (napi)
https://github.com/safetensors/safetensors	safetensors/	bindings/python/ (pyo3)
https://github.com/elastic/elasticsearch	libs/parquet-rs/native/	x-pack/plugin/esql-datasource-parquet-rs/native/
https://github.com/datadog/dd-trace-py	src/native/	src/native_heap_gotter/
https://github.com/wandb/wandb	parquet-rust-wrapper/	experimental/rust-sdk/, xpu/
https://github.com/facebook/watchman	watchman/cli/	watchman/rust/serde_bser/, watchman/rust/watchman_client/
https://github.com/lief-project/lief	tools/	api/rust/crates/ (workspace)
https://github.com/google/flatbuffers	rust/flatbuffers/	rust/flexbuffers/, rust/reflection/

Separately, https://github.com/eventual-inc/daft has a root Cargo.toml (workspace, 70+ members) that brief does not list; manifests[] contains the root Cargo.lock and three member crates but not the root Cargo.toml:

$ brief --json https://github.com/eventual-inc/daft | jq '[.manifests[]|select(.ecosystem=="cargo")|.path]'
["Cargo.lock","src/daft-ext/Cargo.toml","src/daft-ext-macros/Cargo.toml","src/daft-functions-json/Cargo.toml"]

A root manifest should always appear regardless of the nested-detection path.

The current walk seems to seed from the first .rs hit and stop once it reaches a Cargo.toml. Collecting every Cargo.toml reachable within -scan-depth and then pruning those that are workspace members of an already-found root would cover these without also listing every member manifest.