bug: Rust crates that depend on `qdrant-client` break trying to build docs

Logs: https://docs.rs/crate/rig-qdrant/0.1.23/builds/2442024

From docs.rs:

Most of the sandbox is a read-only file system, including the source directory of your crate and its dependencies. If your build.rs generates files that are relevant for documentation, consider writing to the cargo output directory, passed in the environment variable OUT_DIR.

Looks like the qdrant-client build.rs file writes to what would be considered a read-only part of the sandbox (./tests, ...), breaking the docs build.

We can probably fix this by writing the following at the start of the build.rs fn main():

if std::env::var("DOCS_RS").is_ok() {
    return;
}

I am quite keen to get this fixed as Rig (which I maintain) is starting to become quite a heavily used library.

Inspect build.rs and the docs.rs build log linked in the issue, then check how the build behaves when DOCS_RS is set. Reproduce the failure with the documented crate build if possible; done means qdrant-client and dependent crates build their documentation successfully in the docs.rs sandbox.