fix(idempotency): resolve tech debt issues with falsy responses and Redis persistency (#8176)

* fix(idempotency): fix str(None) producing "None" string in Redis persistence

Replace str(item.get(...)) with item.get(...) to avoid storing the
string "None" when a value is missing from Redis hash map.

When data_attr or validation_key_attr is missing from Redis,
item.get() returns None. Wrapping with str() converts it to the
string "None" which is incorrect. Now correctly returns None.

Part of #8090

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

* refactor(idempotency): extract duplicated idempotency key null-check into helper method

Replace 4 identical null-check blocks across save_success, save_inprogress, delete_record, and get_record with a single helper method _get_idempotency_key_or_return_none() to reduce code duplication.

The helper encapsulates the pattern of calling _get_hashed_idempotency_key() and returning None early if the key is None, keeping each method cleaner and easier to read.

Part of #8090

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

* test(idempotency): add unit tests for tech debt fixes in issue #8090

Fix 1 - str(None) in Redis _item_to_data_record:
- Missing data_attr returns None not string "None"
- Existing data_attr returns value correctly
- Demonstrates old bug vs new correct behavior

Fix 2 - _get_idempotency_key_or_return_none helper:
- Returns None when key is None
- Returns key string when key exists
- Correctly used in save_success, save_inprogress,
  delete_record, and get_record (all return None early)

Part of #8090

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

* fix(idempotency): fix falsy response handling and inconsistent status constant

Fix 1 - Falsy response handling in _get_function_response(): Replace `if response else None` with `if response is not None else None`. So valid falsy return values (0, False, {}, [], "") are correctly   serialized and stored instead of being silently discarded.

Fix 2 - Inconsistent status constant in _process_idempotency():
Replace string literal "INPROGRESS" with STATUS_CONSTANTS["INPROGRESS"] for consistency with the rest of the codebase.

Part of #8090

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

* refactor(idempotency): revert helper method - restore original inline null-check pattern

Per Leandro Damascena's feedback: _get_idempotency_key_or_return_none() helper added
indirection without reducing duplication since the if None: return None check remained in all 4 callers anyway.

Restored original inline 3-line pattern in save_success, save_inprogress, delete_record, and get_record which is clearer and instantly readable.

Part of #8090

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

* test(idempotency): remove standalone test file per maintainer feedback

Tests should be added to existing test files following established patterns, not in new standalone files. The Redis fix will be tested in
_redis/test_redis_layer.py next to the existing test_item_to_datarecord_conversion.

Part of #8090

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

* test(idempotency): add regression test for str(None) fix in _item_to_data_record

Added single test next to existing test_item_to_datarecord_conversion to verify missing Redis attributes return None instead of string "None".

Follows existing test patterns using fixtures instead of MagicMock.

Part of #8090

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

* fix(idempotency): fix ruff formatting - remove trailing whitespace in base.py

Remove trailing whitespace on blank line between is_missing_idempotency_key
and _get_hashed_payload methods to pass ruff format check.

Part of #8090

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

* fix(idempotency): fix test fixture name and trailing whitespace in test_redis_layer.py

- Fix fixture name from persistence_store_redis to persistence_store_standalone_redis
  to match existing fixture defined in the test file
- Remove trailing whitespace on blank line after test function to pass ruff format check

Part of #8090

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

* fix: small changes

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Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>
Co-authored-by: Leandro Damascena <lcdama@amazon.pt>