Add backtrace to logged exception

[Flamefire]

(created using eb --new-pr)

This improves debugging issues/crashes as it not only includes the location of the error but also the backtrace.
This is especially useful for very generic errors like the template-resolving failure where it would be important to know where exactly it failed to resolve and not the location of the error (inside the resolve function)

The log now looks like this:

== 2025-11-14 17:17:03,179 build_log.py:226 ERROR EasyBuild encountered an error (at easybuild/base/exceptions.py:140 in __init__): get_software_root software root for M4 was not found in environment (at easybuild/tools/toolchain/toolchain.py:443 in _get_software_root)
Callstack: 
        easybuild/tools/toolchain/toolchain.py:443 in _get_software_root
        easybuild/tools/toolchain/toolchain.py:435 in _get_software_multiple
        easybuild/tools/toolchain/toolchain.py:423 in get_software_root
        easybuild/tools/toolchain/toolchain.py:1153 in _add_dependency_variables
        easybuild/tools/toolchain/toolchain.py:899 in prepare
        easybuild/framework/easyblock.py:2988 in prepare_step
        easybuild/easyblocks/generic/cargo.py:468 in prepare_step
        easybuild/framework/easyblock.py:4753 in run_step
        easybuild/framework/easyblock.py:4912 in run_all_steps
        easybuild/framework/easyblock.py:5099 in build_and_install_one
        easybuild/main.py:163 in build_and_install_software
        easybuild/main.py:596 in process_eb_args
        easybuild/main.py:780 in main
        easybuild/main.py:829 in main_with_hooks
        easybuild/main.py:843 in <module>

"Callstack" because the most recent call is at the top