fix: value-based equality and hashCode for BleCharacteristic

[xianjianlf2]

Problem

BleCharacteristic.operator== compares the properties list with !=, which is List identity comparison in Dart, and hashCode uses properties.hashCode, which is also identity-based. As a result, two characteristics with identical content are never equal unless they share the exact same list instance:

final a = BleCharacteristic("180A", [CharacteristicProperty.read]);
final b = BleCharacteristic("180A", [CharacteristicProperty.read]);
print(a == b); // false — but they are logically equal

This breaks the ==/hashCode contract and makes BleCharacteristic unreliable as a Set element or Map key (e.g. deduplicating characteristics across discovery runs).

Fix

• operator== now compares properties with listEquals.
• hashCode now uses Object.hashAll(properties).

This matches the pattern already used by ManufacturerData in this package.

Testing

• Added test/ble_characteristic_equality_test.dart covering: equal content ⇒ equal + same hash, differing properties ⇒ unequal, differing uuid ⇒ unequal, and Set/Map key usage.
• Ran flutter test test/ble_characteristic_equality_test.dart locally (Flutter 3.44.1 / Dart 3.12.1): 4 tests, all passing.

Changelog

Added an entry under the unreleased 2.1.1 section in CHANGELOG.md.

[gemini-code-assist]

Code Review

This pull request fixes the equality and hashCode implementation of BleCharacteristic to compare properties by value using listEquals and Object.hashAll, and adds corresponding unit tests. The reviewer suggested using Object.hash instead of the bitwise XOR (^) operator to combine hash codes to prevent potential hash collisions.

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[gemini-code-assist]

Using the bitwise XOR (^) operator to combine hash codes is prone to hash collisions (e.g., if fields have identical hash values, they cancel each other out). It is a best practice in Dart to use Object.hash to combine multiple hash codes safely.

Suggested change

	int get hashCode =>
	uuid.hashCode ^ Object.hashAll(properties) ^ metaData.hashCode;
	int get hashCode => Object.hash(
	uuid,
	Object.hashAll(properties),
	metaData,
	);

[fotiDim]

@xianjianlf2 could you please check this comment?