* General code cleanup and rename variables to use a consistent style.
* Removes the disconnect timer and will use the BLE_GAP_EVENT_TERM_FAILURE event to handle failed disconnects.
* `NimBLEClient::getConnId` has been renamed to `getConnHandle` to be consistent with bluetooth terminology.
* `NimBLEClient::disconnect` now returns a `bool = true on success` instead of an int to be consistent with the rest of the library.
* `NimBLEClient::setPeerAddress` now returns a bool, true on success.
* `NimBLEClientCallbacks::onConfirmPIN` renamed to `NimBLEClientCallbacks::onConfirmPasskey` to be consistent with bluetooth terminology.
* `NimBLEClient::setDataLen` now returns bool, true if successful.
* `NimBLEClient::updateConnParams` now returns bool, true if successful.
* `NimBLEClient::getServices` now returns a const reference to std::vector<NimBLERemoteService*> instead of a pointer to the internal vector.
Refactor attributes to reduce code duplication and improve maintainability.
* Add attribute base classes to provide common code.
* Add const where possible to functions and parameters.
* `NimBLECharacteristic::notify` no longer takes a `bool is_notification` parameter, instead `indicate()` should be called to send indications.
* `NimBLECharacteristic::indicate` now takes the same parameters as `notify`.
* `NimBLECharacteristicCallbacks` and `NimBLEDescriptorCallbacks` methods now take `const NimBLEConnInfo&` instead of non-const.
* `NimBLECharacteristic::onNotify` callback removed as unnecessary, the library does not call notify without app input.
* `NimBLERemoteCharacteristic::getRemoteService` now returns a `const NimBLERemoteService*` instead of non-const.
* Add NimBLEUUID constructor that takes a reference to `ble_uuid_any_t`.
* `NimBLERemoteService::getCharacteristics` now returns a `const std::vector<NimBLERemoteCharacteristic*>&` instead of non-const `std::vector<NimBLERemoteCharacteristic*>*`
* `NimBLERemoteService::getValue` now returns `NimBLEAttValue` instead of `std::string`
* `NimBLEService::getCharacteristics` now returns a `const std::vector<NimBLECharacteristic*>&` instead of a copy of std::vector<NimBLECharacteristic *>.
* Remove const requirement for NimBLEConnInfo parameter in callbacks.
Const is unnecessary as the data can't be changed by application code.
* Change NimBLERemoteCharacteristic::getRemoteService to return const pointer.
