fix crash in Cargo easyblock when no crates are specified

[Flamefire]

The extract step accesses self.crates but that is not set when the 'crates' key in the EasyConfig is not set yielding

AttributeError: 'CargoPythonPackage' object has no attribute 'crates'

While this usecase is rare and might not make much sense we shouldn't crash so initialize this property to an empty list.

• Requires fix double initialization of Cargo by CargoPythonPackage by removing incorrect custom __init__ implementation + fix use of super() in PALM easyblock (since that doesn't work with Python 2.7) #3406

[Flamefire]

Test report by @Flamefire

Overview of tested easyconfigs (in order)

CargoPythonPackage

• SUCCESS bcrypt-4.1.3-GCCcore-13.2.0.eb
• SUCCESS tiktoken-0.7.0-GCCcore-12.3.0.eb

CargoPythonBundle

• SUCCESS jiter-0.4.1-GCCcore-12.3.0.eb
• SUCCESS pydantic-2.7.4-GCCcore-13.2.0.eb

Cargo

• SUCCESS SKA2-0.3.7-GCCcore-12.2.0.eb
• SUCCESS ripunzip-0.4.0.eb
• SUCCESS alevin-fry-0.9.0-GCCcore-13.2.0.eb

Build succeeded for 7 out of 7 (7 easyconfigs in total)
i7024 - Linux Rocky Linux 8.9 (Green Obsidian), x86_64, AMD EPYC 7702 64-Core Processor (zen2), Python 3.8.17
See https://gist.github.com/Flamefire/104721135e3f9c427bfbd39dc2454759 for a full test report.

[boegel]

@Flamefire Please sync with develop now #3406 is merged?

[Flamefire]

Done but might need new tests as I removed the reset of self.cfg['crates'] which shouldn't be required anymore.

I tested with easybuilders/easybuild-easyconfigs#21143 for a dummy state representing a PR of possibly affected ECs

[Micket]

lgtm

[Micket]

Test report by @Micket

Overview of tested easyconfigs (in order)

• SUCCESS cryptography-42.0.8-GCCcore-13.3.0.eb

Build succeeded for 1 out of 1 (1 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/221bbe83fc1941d0b350b0020d17f2d4 for a full test report.

[Micket]

I tested with offline = False and no crates and it worked.