fix unresolved templates in modextravars/modextrapaths of Bundle components

[Flamefire]

(created using eb --new-pr)

The following example EC causes an unresolved templates error due to modextravars/paths even with --module-only

easyblock = 'Bundle'

name = 'Test'
version = '1.0.0'

description = "Test modextravars with installdir template"
homepage = ''

toolchain = SYSTEM

default_easyblock = 'Binary'
components = [
    ('zlib', '1.3.1', {
	'install_cmd': 'echo "Hello World"',
	'source_urls': ['https://zlib.net/fossils/'],
	'sources': [SOURCELOWER_TAR_GZ],
    }),
]

modextravars = { 'TEST_VAR': '%(installdir)s' }
modextrapaths = { 'TEST_DIR': '%(installdir)s' }

moduleclass = 'lib'

Issue is that those parameters are copied to each component and then the make_module_step for each component is called without the required templates being available. Example dict:
{'arch': 'x86_64', 'rpath_enabled': 'false', 'sysroot': '', 'software_commit': '', 'nameletter': 'z', 'toolchain_name': 'system', 'toolchain_version': 'system', 'version_major': '1', 'version_minor': '3', 'version_major_minor': '1.3', 'bitbucket_account': 'zlib', 'github_account': 'zlib', 'name': 'zlib', 'version': '1.3.1', 'versionsuffix': '', 'versionprefix': '', 'namelower': 'zlib', 'nameletterlower': 'z', 'module_name': 'Test/1.0.0'}

Even when suppressing the error the resulting module would be wrong as it contains the unresolved template.
Due to another bug those values don't turn up in module files.

So those 2 parameters must also not be inherited.

I refactored the code to loop over all values to reset and use the explicit default value instead of e.g. an empty list.
That could actually have been an issue because a = b = [] does only create a single list, so modifying source_urls modifies sources too.
Doesn't seem to be an issue so far but better to fix this now.
The loop makes it easier to extend this to more parameters as required.

[Flamefire]

Test report by @Flamefire

Overview of tested easyconfigs (in order)

• SUCCESS Wayland-1.23.0-GCCcore-13.3.0.eb
• SUCCESS FlexiBLAS-3.2.0-GCC-11.3.0.eb
• SUCCESS SentencePiece-0.2.0-GCC-13.2.0.eb
• SUCCESS at-spi2-atk-2.38.0-GCCcore-13.3.0.eb
• SUCCESS libepoxy-1.5.10-GCCcore-13.3.0.eb
• SUCCESS GTK3-3.24.42-GCCcore-13.3.0.eb

Build succeeded for 6 out of 6 (4 easyconfigs in total)
n1607 - Linux RHEL 8.9 (Ootpa), x86_64, Intel(R) Xeon(R) Platinum 8470 (sapphirerapids), Python 3.9.18
See https://gist.github.com/Flamefire/e5d7cb49f636d08556d28836fb82498f for a full test report.

[boegel]

lgtm