fix: harden exception handling, break ARC cycles, sync license/client

Replace bare except: with CatchableError across storage, query, Raft,
backup, and protocol code so Defects are not swallowed. Break uncollectable
ARC cycles in server shard/gossip callbacks via Server-owned refs and
cursor locals. Align package license with LICENSE (BSD-3-Clause), sync
README version, and point test_all at the canonical clients/nim baradb
client (parseConnectionString + aliases).

tests/config.nims

@@ -1 +1,2 @@
 --path:"../src"
+--path:"../clients/nim/src"

tests/test_all.nim

@@ -31,7 +31,11 @@ import barabadb/query/udf
 import barabadb/vector/simd
 import barabadb/core/crossmodal
 import barabadb/core/gossip
-import barabadb/client/client
+# Canonical Nim client (not the deprecated src/barabadb/client).
+# Selective import avoids WireValue clash with barabadb/protocol/wire.
+from baradb/client import parseConnectionString, defaultClientConfig, newBaraClient,
+  newQueryBuilder, newSyncClient, BaraClient, QueryBuilder, ClientConfig, SyncClient,
+  select, `from`, where, join, leftJoin, groupBy, having, orderBy, limit, offset, build, exec
 import barabadb/client/fileops
 import barabadb/fts/multilang as mlang
 import barabadb/protocol/zerocopy

tests/test_schema_persist.nim

@@ -6,7 +6,6 @@ import std/tables
 import barabadb/storage/lsm
 import barabadb/query/executor
 import barabadb/query/parser
-import barabadb/query/ast
 
 proc execSql(ctx: ExecutionContext, sql: string): ExecResult =
   let node = parse(sql)

tests/test_storage_hardening.nim

@@ -1,7 +1,6 @@
 ## Focused storage hardening tests (avoids full suite compile issues)
 import std/unittest
 import std/os
-import std/strutils
 import std/locks
 import barabadb/storage/lsm
 import barabadb/storage/rwlock