fix(storage): do not enforce DirectPath for Rapid buckets

[alleaditya]

Description

In GCSFuse, createGRPCClientHandle in internal/storage/storage_handle.go previously attached experimental.WithDirectConnectivityEnforced() unconditionally for all gRPC clients.

For Rapid buckets, DirectPath is not supported/enforced. Forcing DirectPath headers causes GCS servers to reject non-DirectPath requests once DirectPath enforcement is active.

This change:

1. Conditionally omits experimental.WithDirectConnectivityEnforced() when isBucketRapid is true.
2. Skips DirectPath connectivity verification (verifyDirectPathConnectivity) for Rapid buckets to avoid unnecessary dummy Stat API call retries, latency, and warning logs.
3. Adds dedicated unit test cases for Rapid vs Non-Rapid bucket gRPC client handle initialization in internal/storage/storage_handle_test.go.

Link to the issue in case of a bug fix.

Fixes b/541764145

Testing details

1. Manual - Ran verification script scratch/verify_grpc_headers.sh confirming header and DirectPath handling for Rapid vs Non-Rapid buckets.
2. Unit tests - Added TestCreateGRPCClientHandle_RapidBucket and TestCreateGRPCClientHandle_NonRapidBucket in ./internal/storage. Tests pass cleanly (0.00s execution for Rapid bucket).
3. Integration tests - Executed storage package test suite (go test -v ./internal/storage).

Branch	File Size	Read BW	Write BW	RandRead BW	RandWrite BW
Master	0.25MiB	546.8MiB/s	1.26MiB/s	72.64MiB/s	1.27MiB/s
PR	0.25MiB	543.38MiB/s	1.29MiB/s	71.39MiB/s	1.26MiB/s
Master	48.828MiB	4454.94MiB/s	72.86MiB/s	1463.0MiB/s	62.66MiB/s
PR	48.828MiB	4437.52MiB/s	75.43MiB/s	1498.43MiB/s	75.68MiB/s
Master	976.562MiB	4463.69MiB/s	33.9MiB/s	698.35MiB/s	39.37MiB/s
PR	976.562MiB	4493.43MiB/s	37.92MiB/s	1085.05MiB/s	39.9MiB/s

Any backward incompatible change? If so, please explain.

No

[gemini-code-assist]

Code Review

This pull request updates createGRPCClientHandle to skip DirectPath enforcement and verification for rapid buckets, while also correcting the casing of the isBucketRapid parameter. Additionally, unit tests are added to verify this behavior. The feedback suggests using require.NoError and require.NotNil in the new tests to fail immediately and simplify the client cleanup logic.

[meet2mky]

How do you enforce the direct path for rapid when customer sets direct-path-only

gcsfuse/cfg/params.yaml

Line 693 in a3cca53

Options: 'direct-path-only' (fail if unavailable), 'direct-path-with-fallback' (always fallback to HTTP/1 when direct path is not available).

@vadlakondaswetha This is not going to be handled correctly if this is not enforced. We have to fix the fallback here.