feat: add GCS auto-registration via ctor hooks

[ethan-tyler]

Description

As of today, the Rust meta-crate re-exports the storage crates but never calls their register_handlers helpers. That means every Rust binary still has to remember to call deltalake::gcp::register_handlers(None) (and the equivalents for S3/Azure/etc.) before using cloud URIs, even though the Python bindings auto-register. This PR brings the meta-crate to parity so DeltaOps::try_from_uri("gs://…") works out of the box when the gcs feature is enabled.

Problem

• Users of the deltalake crate must manually register each storage backend before working with gs://, s3://, abfss://, etc.

• Forgetting the call leads to DeltaTableError::InvalidTableLocation("Unknown scheme: gs"), which blocks workflows like DataFusion writers on GCS.

• Docs/examples didn’t make it obvious when manual registration was still required.

Solution

• Add feature-gated ctor hooks in crates/deltalake/src/lib.rs that call register_handlers(None) for AWS, Azure, GCS, HDFS, LakeFS, and Unity as soon as their features are enabled.

• Pull in the lightweight ctor = "0.2" dependency so the hooks run at startup.

• Add a small regression test that exercises DeltaTableBuilder::from_uri("gs://…") with the gcs feature to guard against regressions.

• Update the GCS integration docs and changelog to explain that the meta-crate now auto-registers backends while deltalake-core users still need to call the storage crates explicitly.

Changes

• crates/deltalake/src/lib.rs: new #[ctor::ctor] modules for s3, azure, gcs, hdfs, lakefs, and unity.

• crates/deltalake/Cargo.toml: add ctor dependency.

• crates/deltalake/tests/gcs_auto_registration.rs: new smoke tests for gs:// URI recognition when the gcs feature is enabled.

• docs/integrations/object-storage/gcs.md & CHANGELOG.md: document the auto-registration behavior.

Testing

• cargo check -p deltalake --all-features
• cargo test -p deltalake --features gcs
• cargo test --test gcs_auto_registration --features gcs
• cargo build --example pharma_pipeline_gcs --features gcs,datafusion

Documentation

• docs/integrations/object-storage/gcs.md
• CHANGELOG.md

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.93%. Comparing base (16621c4) to head (c1f704f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3923      +/-   ##
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+ Coverage   73.91%   73.93%   +0.02%     
==========================================
  Files         152      153       +1     
  Lines       39465    39455      -10     
  Branches    39465    39455      -10     
==========================================
+ Hits        29170    29172       +2     
+ Misses       8971     8960      -11     
+ Partials     1324     1323       -1     

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[ion-elgreco]

Lgtm, can you fix the markdown links check and add tests for each store

[ethan-tyler]

@ion-elgreco Fixed both items:

• Added crates/deltalake/tests/storage_auto_registration.rs, which exercises each scheme

• Updated docs/integrations/object-storage/gcs.md to link to the GitHub changelog directly

Lmk if you’d like any other schemes covered.