New features

• feat: add CUDA kernels that calculate length/sum by @ManasviGoyal in #2992
• feat: add variable length loop kernels by @ManasviGoyal in #3003
• feat: make ak.mean and ak.count differentiable by @Saransh-cpp in #3020

Bug-fixes and performance

• fix: remove redundant(?) Jax.is_tracer_type check in _layout by @Saransh-cpp in #3013
• fix: throw more meaningful error message for non-NumPy buffers by @agoose77 in #3026
• fix: proper typetracer array slicing in BitMaskedArray by @agoose77 in #3028
• fix: ak.flatten on BitMaskedArray by @agoose77 in #3034
• fix: performance of ufunc resolution for non-nominal signatures by @agoose77 in #3030

Other

• test: update tests-cuda to use 'ByteMaskedArray.simplified' by @jpivarski in #3024
• ci: Add nightly upload of wheels to Anaconda Cloud by @matthewfeickert in #3012
• ci: Update scientific-python/upload-nightly-action from 0.3.0 to 0.4.0 by @matthewfeickert in #3031
• ci: Upload nightly wheels to scientific-python-nightly-wheels org by @matthewfeickert in #3032
• chore: update pre-commit hooks by @pre-commit-ci in #3005
• chore: fix ruff warnings by @agoose77 in #3010
• chore: update pre-commit hooks by @pre-commit-ci in #3022
• chore: figuring out how to implement ak.from_cudf by @jpivarski in #3027
• chore: update pre-commit hooks by @pre-commit-ci in #3029
• chore(deps): bump the actions group with 1 update by @dependabot in #3035
• chore(deps): bump the actions group with 2 updates by @dependabot in #3037

Full Changelog: v2.6.1...v2.6.2