refactor: replace fixed batch size with dynamic flushing based on count and memory

Replace the old fixed batch-size mechanism in Distribute with a dynamic strategy that flushes batches when either BatchSizeMax() sequences or BatchMem() bytes are reached per key. This aligns with the RebatchBySize strategy and removes the optional sizes parameter. Also update related code: simplify Lua wrapper to accept optional capacity, and fix buffer growth logic in worker.go using slices.Grow correctly. Remove unused BatchSize() usage from obidistribute.

pkg/obilua/obiseqslice.go

@@ -31,7 +31,8 @@ func obiseqslice2Lua(interpreter *lua.LState,
 }
 
 func newObiSeqSlice(luaState *lua.LState) int {
-	seqslice := obiseq.NewBioSequenceSlice()
+	capacity := luaState.OptInt(1, 0)
+	seqslice := obiseq.NewBioSequenceSlice(capacity)
 	luaState.Push(obiseqslice2Lua(luaState, seqslice))
 	return 1
 }