Fix async activation retry handling

[fancyboi999]

Problem

Activation providers were still doing synchronous HTTP work from Maigret's async checking pipeline. When a response body matched an activation marker, the checker could block the event loop while refreshing provider tokens.

While verifying the async conversion through the CLI, I also found that the default protocol checkers were shared mutable instances. With concurrent activation retries, one site's retry could reuse another site's prepared URL/headers.

Closes #2671.

Root cause

• ParsingActivator methods used requests directly.
• check_site_for_username() called activation without await.
• process_site_result() had a second synchronous activation block that mutated headers but did not retry the current response.
• maigret() stored checker instances in options["checkers"], so concurrent site checks shared mutable url, headers, method, and payload state.

Solution

• Convert activation methods to async def and use aiohttp.ClientSession.
• Await activation before retrying the site check.
• Remove the duplicate activation block from process_site_result().
• Store protocol checker factories instead of shared checker instances, so each site check gets independent request state.
• Add regression coverage for async activation and concurrent retry isolation.

Validation

Runtime verification through the real CLI with a temporary local Maigret DB and local HTTP server:

• python -m maigret alice ... -n 3
  • exit code: 0
  • elapsed: 1.845s
  • three 1-second activation requests started together and ended together
  • retries returned to their own profile URLs:
    • profile:two:alice:jwt token-two
    • profile:one:alice:jwt token-one
    • profile:three:alice:jwt token-three

Probe:

• python -m maigret alice ... -n 1
  • exit code: 0
  • elapsed: 3.832s
  • activations were serialized and each retry used the matching profile URL.

Additional local checks:

• python -m pytest tests/test_activation.py tests/test_checking.py -q
  • 55 passed, 1 skipped
• python -m pytest -q --ignore=tests/test_submit.py --ignore=tests/test_twitter.py
  • 294 passed, 3 skipped
• .githooks/pre-commit
  • completed after installing Poetry via uv tool install poetry
  • generated only a db_meta.json timestamp update with unchanged data_sha256, so that unrelated timestamp churn is intentionally not included in this PR
• git diff --check
  • passed

Known environment notes:

• tests/test_submit.py has live Google Play / icq.com network dependencies in this environment.
• tests/test_twitter.py live GraphQL probe currently returns HTTP 403.

[soxoj]

@fancyboi999 amazing work, thank you so much! 🚀 👍 🔥
Please, contribute more! ^_^

I'm merging it ✅