Move the distributed bandit out of this repository

[sshaplygin]

Pooling per-epoch statistics across replicas through Valkey or Redis is a
networked coordination subsystem. This library is for measuring adaptive policy
selection, and that subsystem served none of its declared readers: it added a
Redis client, a Lua script, a docker-compose file, a two-engine CI job and
roughly 2,500 lines to a repository whose point is that you can read it in an
evening.

38 files changed, 13 insertions(+), 6015 deletions(-)

Removed

bandit/redis (whole module) · the fleet half of the bandit module
(distributed, coordinate, store, memstore, fingerprint, window,
snapshot, config, errors and their tests) · bench/fleet.go and its test
· docs/fleet.md · docker-compose.yml · the Makefile redis targets · the CI
redis job · the pooling section of docs/evidence.md, which measured the code
being removed.

The bandit module keeps what a single process needs — Thompson, Greedy,
and the Beta sampling behind them. Its go.mod is now as-cache plus testify.

No forwarding pointer

The code is not published anywhere, so the documentation links to nothing: a
link to a repository that does not exist is worse than no link. It stays
reachable in this repository's history at the commit before this one, which is
where anyone reviving it should start.

API-BREAK

The bandit module loses NewDistributed, NewMemStore, Distributed,
MemStore, Store, Config, Mode, EvidenceMode, Snapshot, Role,
Bucket, ArmCounts, ArmEvidence, ArmKey, SyncRequest, SyncResult,
WindowCounts, the ModeLeader/ModeSharedPosterior and
EvidenceAll/EvidenceShadowOnly constants, and the seven sentinel errors
that validated a Config. The bandit/redis module is withdrawn.

Verification

make all   -> Release checks passed, nine modules
git ls-files | xargs grep -lni 'fleet|valkey|go-redis'
           -> CHANGELOG.md (history, untouched) and docs/policies.md
              ("the whole fleet of measurements", a figure of speech)