refactor(services/cos): complete capability override migration

[Xuanwo]

Which issue does this PR close?

Refs #6708.

Rationale for this change

COS still had a service config value that only changed declared capabilities. After #7520, those test/setup differences should be expressed through capability overrides instead of COS-specific config.

What changes are included in this PR?

This PR deprecates enable_versioning as a no-op compatibility shim, declares COS versioning capabilities directly, and migrates the COS behavior setup to OPENDAL_TEST_CAPABILITY_OVERRIDES. The COS test setup also disables write_with_if_not_exists and copy_with_if_not_exists because x-cos-forbid-overwrite only works for buckets that have never enabled versioning.

It also aligns the Go binding's capability FFI layout with the C opendal_capability struct. Go kept a stale extra blocking field, which made Info().GetFullCapability() decode a different struct shape than the C ABI returns and could crash behavior tests.

Are there any user-facing changes?

enable_versioning is now deprecated for COS and no longer changes COS's native capability declaration. COS setups with narrower capability support should override the operator capability instead.

AI Usage Statement

N/A.