Light Gbm: v4.3.0 Release

Changes

💡 New Features

• [CUDA] Add arch=8.9 to CUDA_ARCHS for RTX 40XX @DmitryUlyanov (#6272)

🔨 Breaking

• [cmake] [c++] require CMake 3.18+ @jameslamb (#6260)
• [R-package] remove readRDS.lgb.Booster() and saveRDS.lgb.Booster() @jameslamb (#6246)

🚀 Efficiency Improvement

• [R-package] Remove non-beneficial parallelization @david-cortes (#6209)

🐛 Bug Fixes

• [R-package] [ci] remove unnecessary include in linear_tree_learner (fixes #6264) @jameslamb (#6265)
• [cmake] [CUDA] ignore CUDA-specific source files in non-CUDA builds (fixes #6267) @sabjohnso (#6268)
• [c++] include OpenMP-control files in MSBuild solution file (fixes #6238) @jameslamb (#6251)
• [cmake] [swig] use CMake's built-in file-copying mechanisms instead of 'cp' @jameslamb (#6259)

📖 Documentation

• [docs] Add LightGBMLSS to README @StatMixedML (#6254)
• [ci] [docs] add Oliver to CODEOWNERS @jameslamb (#6247)
• Fix small typo and grammar in docs @arunstar (#6245)

🧰 Maintenance

• [ci] fix conda env creation in 'regular' CI job (fixes #6282) @jameslamb (#6283)
• [R-package] [ci] switch vignettes from 'rmarkdown' to 'markdown' @jameslamb (#6258)
• [python-package] fix mypy error about pandas categorical features @jameslamb (#6253)
• [ci] update issue-locking workflow @jameslamb (#6256)
• [ci] upgrade to GoogleTest v1.14.0 (fixes #5976) @jameslamb (#5981)
• [ci] [R-package] speed up valgrind job @jameslamb (#6237)
• bump development version to 4.2.0.99 @jameslamb (#6241)