Release v0.2.3

Changes

• Add support for Python v3.15 and drop support for v3.11
• Update dependencies and dependency pins across the board
• Upgrade to MyPy v2, adjust for new strict settings, use native parser
• Add support for Visual Studio Code as an IDE
• Use pytest-cov for test coverage, for more consistency
• Fix pytest-testdox output in GHA Windows runner
• Update Read the Docs config to use generic latest Ubuntu runner
• Run the GHA matrix build on free-threaded 3.14t and 3.15t