refactor(redis): typed RedisReply instead of dynamic replies; move RedisConnectionTestFake out of lib #1571

Problem

RedisConnection.sendCommand(List<dynamic> args) -> Future<dynamic> (lib/core/database/redis_connection.dart:391) passes raw redis package replies through. Every caller re-parses them by hand: 9 is List / length == 2 checks in redis_connection.dart alone (scan, getMaxDatabases, hash/zset/stream readers), plus redisReplyInt / RedisBulkValue.fromReply with fallbacks that hide a wrong reply shape (redisReplyInt(result, -1) turns an error into -1).

A Redis error reply and a wrong-type value look the same to callers, and arguments are List<dynamic>, so a non-string argument goes through unchecked.

RedisConnectionTestFake (:817, ~280 lines) lives in lib/ and ships in the release binary.

Fix

• Parse once into a sealed RedisReply (RedisInt, RedisBulk(bytes), RedisSimple, RedisArray, RedisNil, RedisErrorReply) at the sendCommand boundary. Accessors like asInt() / asArray() throw a typed RedisProtocolException on a shape mismatch.
• Typed arguments: List<Object> of String | int | Uint8List | RedisBulkValue, converted in one place (redisCommandArg).
• Move RedisConnectionTestFake to test/ (or lib/testing/ excluded from the app).
• Pure refactor, no behaviour change; do it after fix(redis): explorer views share one socket, so SELECT + command is not atomic; folder delete can hit another DB #1569 (Redis DB-switch fix), which touches the same file.