chore: update version to 9.1.0 (VowpalWabbit#3846)

* chore: update version to 9.1.0

fix: use different syntax for opening namespace for custom formatters

fix: learn/predict exceptions were causing a destructor to throw (Vow…

…palWabbit#3659)

* fix: learn/predict exceptions were causing a destructor to throw

* Update learner.cc

* trigger CI

* fix onethread

refactor: rename file namespaced_features -> namespaced_feature_store (…

…VowpalWabbit#3154)

test: update test to target 8.10.1 code

ci: run CI on release branches (VowpalWabbit#2942)

Update version to 8.10.0 (VowpalWabbit#2912)

Update version to 8.9.2

Update version to 8.9.1

Update version to 8.9.0 (VowpalWabbit#2639)

Co-authored-by: olgavrou <[email protected]>