2.9.0 - Many new synths

Features:

• #438 Added the LegacyLoaderCapability for adaptations that need to load older or non-standard file formats, and documented the new hook in the Adaptation Programming Guide.
• #508 Added the CustomProgramChangeCapability Python binding so adaptations can define their own program change behavior.
• Added a simulated MIDI wire test layer for adaptation tests, covering bank downloads, edit buffer requests, and send-to-synth code paths.
• Exposed the filename currently being processed to Python adaptations, so file-based import logic can make better decisions.

Synths:

• #433 and #72 Added the Kawai K5000 adaptation with bank import support and test data. Heroic effort by @markusschloesser on this what I think is our most complex adpatation yet!
• #517 Added the Roland SE-02 adaptation contributed by @MammaScan. Many thanks for this!
• #501 Improved Korg microKORG/microKORG S bank dump requests from @ilantz by returning the request sequence in the format expected by the C++ sender.
• #460 Korg R3 adaptation added. By now it is possible to get adaptations 100% written by AI by just giving them the manual download. This adds a new GenericKorg python module which can be used for new Korg adaptations to reduce code duplication.
• #464 Roland JD-Xi adaptation added, also 100% AI
• #503 Roland U-20/U-220 adpatation added, also 100% AI.
• Improved the Roland D-50 adaptation and used it to the new mock MIDI tests, extending test coverage.

Bug fixes:

• #520 Improved CMake Python detection with a fallback path and explicit Python 3.12+ version checks. Thanks for @ilantz for this!
• #525 Updated bundled third-party libraries, including JUCE 8.0.12, pybind11 3.0.3, spdlog 1.17.0, fmt 12.1.0, doctest 2.5.2, json 3.12.0, json-schema-validator 2.4.0, ICU, and WinSparkle.
• #524 Updated pytest to 9.0.3.
• #319 Added a docker build step testing that the archlinux version can be built as described by the README. Thanks to @fractalf for the details!
• Hardened the macOS hdiutil retry script and fixed an off-by-one retry loop error.
• Fixed a crash when a program buffer synth returned an empty list of bank descriptors.