feat: LINDEX, LSET, LTRIM, LINSERT, LREM, LPOS list commands

[kacy]

summary

fills critical list command gaps with 6 new commands: LINDEX, LSET, LTRIM, LINSERT, LREM, and LPOS. this completes the list data type coverage alongside the existing LPUSH/RPUSH/LPOP/RPOP/LRANGE/LLEN/BLPOP/BRPOP.

commands added:

• LINDEX — get an element by index (O(n) random access on VecDeque)
• LSET — set the value at a specific index
• LTRIM — trim a list to the specified range (auto-deletes empty keys)
• LINSERT — insert before or after a pivot element (with memory enforcement)
• LREM — remove elements matching a value (forward, reverse, or all)
• LPOS — find positions of matching elements (with RANK/COUNT/MAXLEN options)

full vertical slice per command:

• keyspace methods with comprehensive tests (30 new tests, 59 total list tests)
• RESP3 command parsing with validation
• shard request/response dispatch
• AOF persistence (4 new record types: LSET, LTRIM, LINSERT, LREM)
• AOF recovery replay
• replication stream support
• sharded + concurrent connection handler routing
• cluster slot checking
• CLI autocomplete and help entries

what was tested

• 59 list-specific unit tests covering all methods, edge cases, and error paths
• 406 protocol parser tests (including new command parsers)
• 32 AOF round-trip tests (serialization, deserialization, recovery)
• 14 recovery tests
• 114 CLI tests (including alphabetical ordering fix)
• full cargo build clean across all crates

design considerations

• LPOS COUNT semantics: when COUNT is not specified, the shard fetches at most 1 match and the connection handler returns a single integer (or null). when COUNT is specified (including COUNT 0 for all matches), it returns an array. this matches Redis behavior.
• memory tracking: LSET uses delta-based tracking (old_len vs new_len). LTRIM recomputes full value_size since the change is bulk. LINSERT uses enforce_memory_limit with a defensive re-check after possible eviction of the target key itself.
• borrow safety: scoped blocks release entry borrows before calling self.memory.* methods, avoiding Rust borrow checker conflicts between self.entries and self.memory.
• AOF records: read-only commands (LINDEX, LPOS) don't generate AOF records. write commands only persist on success (LINSERT when n>0, LREM when n>0).