Feature/508 secagg handle error

MR description

Address #508 (closed)

Could not reproduce the bug, but improved failed training handling/error messages for the researcher.

Developer Certificate Of Origin (DCO)

By opening this merge request, you agree the Developer Certificate of Origin (DCO)

This DCO essentially means that:

• you offer the changes under the same license agreement as the project, and
• you have the right to do that,
• you did not steal somebody else’s work.

License

Project code files should begin with these comment lines to help trace their origin:

# This file is originally part of Fed-BioMed
# SPDX-License-Identifier: Apache-2.0

Code files can be reused from another project with a compatible non-contaminating license. They shall retain the original license and copyright mentions. The CREDIT.md file and credit/ directory shall be completed and updated accordingly.

Guidelines for MR review

General:

• give a glance to DoD
• check coding rules and coding style
• check docstrings (eg run tests/docstrings/check_docstrings)

Specific to some cases:

• update all conda envs consistently (development and vpn, Linux and MacOS)
• if modified researcher (eg new attributes in classes) check if breakpoint needs update (breakpoint/load_breakpoint in Experiment(), save_state/load_state in aggregators, strategies, secagg, etc.)