Create an aggregate from subset of messages

[piotr-roslaniec]

Type of PR:

• Bugfix
• Feature

Required reviews:

• 1

What this does:

High-level idea of the changes introduced in this PR. List relevant API changes (if any), as well as related PRs and issues.

Issues fixed/closed:

• Fixes #179
• Fixes #184

Why it's needed:

Explain how this PR fits in the greater context of the NuCypher Network. E.g., if this PR address a nucypher/productdev issue, let reviewers know!

Notes for reviewers:

• Based on #183 - Please review it first
• I will review these changes myself again after merging parent PR

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.56776% with 93 lines in your changes are missing coverage. Please review.

Project coverage is 79.98%. Comparing base (2fe8753) to head (18487e6).

Files	Patch %	Lines
ferveo/src/api.rs	94.34%	38 Missing :warning:
ferveo-tdec/src/decryption.rs	39.13%	14 Missing :warning:
ferveo/src/bindings_python.rs	61.11%	14 Missing :warning:
ferveo/src/bindings_wasm.rs	0.00%	12 Missing :warning:
ferveo/src/dkg.rs	94.38%	5 Missing :warning:
ferveo/src/refresh.rs	98.54%	5 Missing :warning:
ferveo-tdec/src/key_share.rs	50.00%	3 Missing :warning:
ferveo-common/src/keypair.rs	0.00%	1 Missing :warning:
ferveo/src/pvss.rs	99.20%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #185 +/- ## ========================================== + Coverage 78.16% 79.98% +1.81% ========================================== Files 24 24 Lines 5222 5876 +654 ========================================== + Hits 4082 4700 +618 - Misses 1140 1176 +36 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[cygnusv]

Approved as part of the R&R epic. This is currently used as the basis of #186 (still WIP), so any relevant comments can be addressed by #186