pythainer: composable and reusable Docker builders and runners for reproducible research

This release focuses on improving reproducibility, container build expressiveness, and documentation in preparation for the JOSS submission. Highlights Enhanced Docker build support with proper COPY handling and BuildKit RUN --mount support, including SSH agent forwarding. Added Nix support to enable fully reproducible development and build environments. Improved QEMU and profiling examples, including reliable networking and minimal Intel VTune integration. Documentation updates and cleanup following JOSS reviewer feedback. For full details, see the CHANGELOG. What's Changed Add RELEASING.md how-to document by @apaolillo in https://github.com/apaolillo/pythainer/pull/37 Add libslirp as a QEMU dependency by @apaolillo in https://github.com/apaolillo/pythainer/pull/43 Fix: allow Python ≥ 3.10 in install_venv.sh by @matsvanmolle in https://github.com/apaolillo/pythainer/pull/45 Add RUN --mount support and ssh forwarding by @apaolillo in https://github.com/apaolillo/pythainer/pull/44 Avoid 0 UID & GID being passed to docker build by @apaolillo in https://github.com/apaolillo/pythainer/pull/46 Expose mounts to run_multiple build command by @apaolillo in https://github.com/apaolillo/pythainer/pull/47 Delete user by UID instead of UID:GID by @EstAK in https://github.com/apaolillo/pythainer/pull/42 Add minimum support for VTune profiler by @aaronbog in https://github.com/apaolillo/pythainer/pull/14 Improve README.md according to JOSS review by @apaolillo in https://github.com/apaolillo/pythainer/pull/48 Make Docker COPY usable via builder.copy() by @aaronbog in https://github.com/apaolillo/pythainer/pull/28 Add Nix support by @EstAK in https://github.com/apaolillo/pythainer/pull/50 Add source for JOSS'25 paper by @apaolillo in https://github.com/apaolillo/pythainer/pull/38 minor change in paper.md by @danielskatz in https://github.com/apaolillo/pythainer/pull/52 joss: Change bib file capitalization by @apaolillo in https://github.com/apaolillo/pythainer/pull/53 joss: Revert changes in the bib by @apaolillo in https://github.com/apaolillo/pythainer/pull/54 Introduce explicit build context for COPY by @apaolillo in https://github.com/apaolillo/pythainer/pull/49 Release 0.0.6 by @apaolillo in https://github.com/apaolillo/pythainer/pull/55 New Contributors @matsvanmolle made their first contribution in https://github.com/apaolillo/pythainer/pull/45 @EstAK made their first contribution in https://github.com/apaolillo/pythainer/pull/42 @aaronbog made their first contribution in https://github.com/apaolillo/pythainer/pull/14 Full Changelog: https://github.com/apaolillo/pythainer/compare/v0.0.5...v0.0.6