refactor(obj): Implement hierarchical object storage client architecture (DNM)

[aranadive]

What?

Introduce a modular, inheritance-based architecture for object storage
clients to support multiple S3-compatible backends and acceleration paths.

The new hierarchy organizes clients as follows:

+------------------+
| Object Base Type|
+------------------+
          |
          v
+------------------+
| S3 Vanilla Object|
+------------------+
          |
      ----------------------------
      |                          |
      v                          v
+------------------+       +----------------+
|  S3 CRT Object   |       | S3 Accel Object|
+------------------+       +----------------+
                                    |
                                    v
                           +----------------+
                           | Dell OBS Object|
                           +----------------+

Why?

The previous flat architecture made it difficult to extend the object plugin
with new vendor-specific backends and acceleration methods. This refactoring
provides:

• Clean separation of concerns with distinct client types
• Easy addition of new vendor-specific backends (Dell, future vendors)
• Flexible runtime client selection via custom parameters
• Polymorphic interface for simplified transfer logic
• Better code organization matching the inheritance relationships

How?

• Created base/client.h with iObjClient interface defining common operations
  (setExecutor, putObjectAsync, getObjectAsync, checkObjectExists)

• Reorganized S3 clients into subdirectories reflecting inheritance:

  • s3/ - Standard S3 client (awsS3Client) inheriting from iObjClient
  • s3_crt/ - S3 CRT client (awsS3CrtClient) inheriting from awsS3Client
  • s3_accel/ - S3 Accelerated client using CRT implementation
  • s3_accel/dell_obs/ - Dell OBS client with vendor-specific optimizations

• Updated obj_backend to dynamically instantiate clients based on parameters:

  • Default: S3 Vanilla client
  • accelerated=true: S3 Accel client
  • accelerated=true,type=dell: Dell OBS client
  • S3 CRT client now optional (only when crtMinLimit is configured)

• Refactored client member types to use polymorphic iObjClient interface

[github-actions]

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