Fixes introduced when absorbing PR #959 (fast conversation switching):
- _accepts_gzip() now uses getattr() to tolerate _FakeHandler and any
synthesised handler that lacks a .headers attribute (fixes 2 test failures
in test_sprint46.py)
- test_issue401: updated assertion to accept both minified and reformatted
forms of the tool_calls fallback guard (PR reformatted the code)
- test_regressions: updated activeStreamId assertion — PR refactored
data.session references to S.session for direct state access
Co-authored-by: nesquena-hermes <nesquena-hermes@users.noreply.github.com>