-`Future<T>::wait` now returns the resolved value and throws if the Future rejected, rather than returning a `std::variant` and slicing the exception to `std::exception`.
- Added a performance tracing framework via `CESIUM_TRACE_*` macros.
- Added `Future<T>::thenImmediately`.
- Added `AsyncSystem::createThreadPool` and `Future<T>::thenInThreadPool`.
-`Future<T>::thenInWorkerThread` and `Future<T>::thenInMainThread` now arrange for their continuations to be executed immediately when the Future is resolved, if the Future is resolved in the correct thread.
- Moved all request cache database access to a dedicated thread, in order to free up worker threads for parallelizable work.
- Accessing the same Bing Maps layer multiple times in a single application run now reuses the same Bing Maps session instead of starting a new one each time.
-`createAccessorView` now creates an (invalid) `AccessorView` with a standard numeric type on error, rather than creating `AccessorView<nullptr_t>`. This makes it easier to use a simple lambda as the callback.
- Disabled `HTTPLIB_USE_ZLIB_IF_AVAILABLE` and `HTTPLIB_USE_OPENSSL_IF_AVAILABLE` because these libraries are not required for our use for cpp-httplib and they cause problems on some systems.
- Added an `Axis` enum and `AxisTransforms` class for coordinate system transforms
- Added support for the legacy `gltfUpVector` string property in the `asset` part of tilesets. The up vector is read and passed as an `Axis` in the `extras["gltfUpVector"]` property, so that receivers may rotate the glTF model's up-vector to match the Z-up convention of 3D Tiles.
- Unknown glTF extensions are now deserialized as a `JsonValue`. Previously, they were ignored.
- Added the ability to register glTF extensions for deserialization using `GltReader::registerExtension`.
- Added `GltfReader::setExtensionState`, which can be used to request that an extension not be deserialized or that it be deserialized as a `JsonValue` even though a statically-typed class is available for the extension.
##### Fixes :wrench:
- Gave glTFs created from quantized-mesh terrain tiles a more sensible material with a `metallicFactor` of 0.0 and a `roughnessFactor` of 1.0. Previously the default glTF material was used, which has a `metallicFactor` of 1.0, leading to an undesirable appearance.
- Reported zero-length images as non-errors as `BingMapsRasterOverlay` purposely requests that the Bing servers return a zero-length image for non-existent tiles.
