fix(dist): duplicate group routes in one batch must not throw NPE

[ImDanXie]

Fixes #299

Summary

When a tenant batch contains two identical group (shared subscription) MatchRoutes, batchAddRoute throws NullPointerException and leaves the route cache inconsistent with the KV store.

Baseline: main @ eef5e3a.

Root cause

Group routes record "route to its index in the request" in a Map of MatchRoute to Integer. MatchRoute is a protobuf message and compares by value, so two identical group routes in the same batch collapse into a single entry, keeping only the later index. The earlier index remains null in the Code array:

groupMatchRecords.computeIfAbsent(new GlobalTopicFilter(tenantId, routeDetail.matcher()),
    k -> new HashMap<>()).put(route, i);   // collapses duplicates, keeps later i
...
for (BatchMatchReply.TenantBatch.Code code : codes) {
    batchBuilder.addCode(code);           // NPE on the null slot
}

Normal routes are unaffected - that branch explicitly assigns codes[i] = OK for every index in a loop. The Group branch was missed.

The proto field is documented as a deduplicated list, but the client BatchMatchCall.makeBatch does not deduplicate. The Normal branch already has explicit dedup handling and a test for it (testAddNormalRouteDuplicatedInOneBatchOnlyCountOnceAndRefresh); the Group branch was missed.

Consequence

The NPE is thrown before MutationResult is returned, but rangeWriter.done() still commits the buffered writes (normal routes + RouteGroup records land in KV), while the co-processor post-actions (routeCache.refresh, deliverExecutorGroup.refreshOrderedSharedSubRoutes, tenant counters, refreshFact) never execute. The batch is reported as ERROR to the client while the route cache remains inconsistent with the KV store until the cache expires - during which publishes are routed using stale data.

Fix

Record all positions for a route rather than only the last one - the value type of both group maps changes from Integer to List of Integer, and the consumer assigns the computed code to every recorded index. The same change applies to delGroupMatchRecords in batchRemoveRoute.

Testing

Two symmetric regression tests in DistWorkerCoProcTest:

• testAddGroupRouteDuplicatedInOneBatchAllPositionsGetOk - add path: two identical group routes, both positions must receive OK.
• testRemoveGroupRouteDuplicatedInOneBatchAllPositionsGetOk - unmatch path: two identical group MatchRoutes; the reader returns a RouteGroup protobuf containing the receiver, so the removal path is exercised.

Control experiment: on unfixed code both tests fail (NPE / null slot); with the fix all 19 tests in DistWorkerCoProcTest pass.