Add FIT persistency scenarios: supported datatypes

[Subramanian-K812]

Implements feature integration tests verifying persistency requirements for KVS datatype
support, default value loading, and reset-to-default behaviour. Both Rust and C++ scenario
implementations are provided with full parity.

New test scenarios (Rust + C++):

• persistency.supported_datatypes.all_value_types — verify all nine KVS value types
  (i32, u32, i64, u64, f64, bool, str, arr, obj) coexist in a single flushed snapshot
• persistency.supported_datatypes.all_types_utf8 — verify all value types stored under
  ASCII, emoji, and Greek key names are all present in a single snapshot
• persistency.default_values.checksum — verify adler32 hash file is written and matches
  the snapshot bytes after flush
• persistency.default_values.partial_override — verify only the explicitly written key
  appears in the snapshot when a defaults file provides more keys
• persistency.default_values.get_default_value — verify get_value returns the default
  value for a key provisioned via the defaults file but never explicitly set
• persistency.default_values.selective_reset — verify reset_key on even-indexed keys
  reverts them to absent while odd-indexed keys keep their override values
• persistency.default_values.full_reset — verify reset() clears all written keys and
  that keys written after reset are correctly persisted
• persistency.default_values_ignored — verify KVS ignores defaults when configured with
  KvsDefaults::Ignored
• persistency.utf8_defaults — verify UTF-8 encoded keys with provisioned defaults load,
  report default state, and accept overrides correctly
• persistency.utf8_default_value_get — verify get_default_value retrieves the correct
  value for a UTF-8 emoji key provisioned via the defaults file
• persistency.multi_instance_isolation — verify that default values loaded for one KVS
  instance do not leak into a second instance sharing the same working directory
• persistency.reset_to_default — verify reset_to_default persists correct values and
  leaves other keys unchanged

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Scenarios

Rust & C++ (parity implementations)

Scenario Name	Test Class	Test File
persistency.supported_datatypes.all_value_types	TestAllValueTypes	test_datatype_support.py
persistency.supported_datatypes.all_types_utf8	TestAllTypesWithUtf8Keys	test_combined_requirements.py
persistency.default_values_ignored	TestDefaultValuesIgnored	test_default_values.py
persistency.default_values.checksum	TestDefaultValuesChecksum	test_default_values.py
persistency.default_values.checksum	TestDefaultValuesMissingDefaultsFile	test_default_values.py
persistency.default_values.checksum	TestDefaultValuesMalformedDefaultsFile	test_default_values.py
persistency.default_values.checksum	TestOptionalModeWithoutDefaults	test_default_values.py
persistency.default_values.partial_override	TestPartialOverrideSnapshot	test_combined_requirements.py
persistency.default_values.get_default_value	TestGetDefaultValue	test_default_values.py
persistency.default_values.selective_reset	TestSelectiveReset	test_default_values.py
persistency.default_values.full_reset	TestFullReset	test_default_values.py
persistency.utf8_defaults	TestUtf8KeysWithDefaults	test_combined_requirements.py
persistency.utf8_default_value_get	TestUtf8DefaultValueGet	test_combined_requirements.py
persistency.multi_instance_isolation	TestMultiInstanceDefaultIsolation	test_default_values.py
persistency.reset_to_default	TestResetToDefault	test_reset_to_default.py

---

Requirements Traceability

Test Class	Requirement IDs
TestAllValueTypes	feat_req__persistency__support_datatype_value feat_req__persistency__support_datatype_keys feat_req__persistency__store_data
TestAllTypesWithUtf8Keys	feat_req__persistency__support_datatype_keys feat_req__persistency__support_datatype_value feat_req__persistency__store_data
TestDefaultValuesIgnored	feat_req__persistency__default_values feat_req__persistency__default_value_get
TestDefaultValuesChecksum	feat_req__persistency__default_values
TestDefaultValuesMissingDefaultsFile	feat_req__persistency__default_values feat_req__persistency__default_value_file
TestDefaultValuesMalformedDefaultsFile	feat_req__persistency__default_values feat_req__persistency__default_value_file
TestOptionalModeWithoutDefaults	feat_req__persistency__default_values feat_req__persistency__default_value_file feat_req__persistency__store_data
TestPartialOverrideSnapshot	feat_req__persistency__default_values feat_req__persistency__default_value_file feat_req__persistency__store_data
TestGetDefaultValue	feat_req__persistency__default_value_get feat_req__persistency__default_values feat_req__persistency__default_value_file
TestSelectiveReset	feat_req__persistency__reset_to_default feat_req__persistency__default_values feat_req__persistency__default_value_file feat_req__persistency__store_data
TestFullReset	feat_req__persistency__reset_to_default feat_req__persistency__default_values feat_req__persistency__default_value_file feat_req__persistency__store_data
TestUtf8KeysWithDefaults	feat_req__persistency__support_datatype_keys feat_req__persistency__default_values feat_req__persistency__default_value_file
TestUtf8DefaultValueGet	feat_req__persistency__default_value_get feat_req__persistency__support_datatype_keys
TestMultiInstanceDefaultIsolation	feat_req__persistency__default_values feat_req__persistency__multiple_kvs
TestResetToDefault	feat_req__persistency__reset_to_default