use PYPI_SOURCE constant in generic PythonPackage easyblock + custom easyblock for Python

[Flamefire]

Required after the conversion in

• convert template constant lists to dicts and export the constants by name easybuild-framework#4595

[boegel]

lgtm (but requires that easybuilders/easybuild-framework#4595 is merged first)

[Micket]

Test report by @Micket

Overview of tested easyconfigs (in order)

• SUCCESS cryptography-42.0.8-GCCcore-13.3.0.eb
• SUCCESS Python-3.12.3-GCCcore-13.3.0.eb
• SUCCESS Python-bundle-PyPI-2024.06-GCCcore-13.3.0.eb
• SUCCESS Mako-1.3.5-GCCcore-13.3.0.eb

Build succeeded for 4 out of 4 (4 easyconfigs in total)
alvis-skylake-build - Linux Rocky Linux 8.9, x86_64, Intel Xeon Processor (Skylake, IBRS, no TSX), Python 3.6.8
See https://gist.github.com/Micket/75149b61849bb923d4984da7566645a1 for a full test report.

[Micket]

Test report by @Micket

Overview of tested easyconfigs (in order)

• SUCCESS libyaml-0.2.5-GCCcore-13.3.0.eb
• FAIL (build issue) LibTIFF-4.6.0-GCCcore-13.3.0.eb (partial log available at https://gist.github.com/Micket/edd61aa41e513f140504db3171f10c3e)
• SUCCESS Zip-3.0-GCCcore-13.3.0.eb
• SUCCESS virtualenv-20.26.2-GCCcore-13.3.0.eb
• SUCCESS Eigen-3.4.0-GCCcore-13.3.0.eb

Build succeeded for 4 out of 5 (5 easyconfigs in total)
vera-skylake-build - Linux Rocky Linux 8.9, x86_64, Intel Xeon Processor (Skylake, IBRS, no TSX), Python 3.6.8
See https://gist.github.com/Micket/26d1d54923e367c8f896325afa14ba39 for a full test report.

(ignore that libtiff issue, new test report coming)

[Micket]

Test report by @Micket

Overview of tested easyconfigs (in order)

• SUCCESS jbigkit-2.1-GCCcore-13.3.0.eb
• SUCCESS NASM-2.16.03-GCCcore-13.3.0.eb
• SUCCESS libjpeg-turbo-3.0.1-GCCcore-13.3.0.eb
• SUCCESS libdeflate-1.20-GCCcore-13.3.0.eb
• SUCCESS LibTIFF-4.6.0-GCCcore-13.3.0.eb

Build succeeded for 5 out of 5 (1 easyconfigs in total)
vera-skylake-build - Linux Rocky Linux 8.9, x86_64, Intel Xeon Processor (Skylake, IBRS, no TSX), Python 3.6.8
See https://gist.github.com/Micket/7c44898133382cde1731f0331e5772d1 for a full test report.

[Micket]

lgtm