Split the old locking_tx_datastore (#757)

* datastore: extract SequencesState

* datastore: extract tx_state

* datastore: extract committed_state & iter

* datastore: extract mut_tx

* cargo fmt

* move some pure AV/AT sats logic to sats

* pacify lints and cargo fmt

* datastore: iter -> state_view + move in StateView

Author: Centril

crates/core/src/db/datastore/locking_tx_datastore/committed_state.rs

@@ -1,4 +1,6 @@
+use spacetimedb_primitives::SequenceId;
 use spacetimedb_sats::db::def::SequenceSchema;
+use std::collections::HashMap;
 
 pub struct Sequence {
     schema: SequenceSchema,
@@ -87,3 +89,23 @@ impl Sequence {
         self.schema.allocated = allocated;
     }
 }
+
+/// A map of [`SequenceId`] -> [`Sequence`].
+#[derive(Default)]
+pub struct SequencesState {
+    sequences: HashMap<SequenceId, Sequence>,
+}
+
+impl SequencesState {
+    pub fn get_sequence_mut(&mut self, seq_id: SequenceId) -> Option<&mut Sequence> {
+        self.sequences.get_mut(&seq_id)
+    }
+
+    pub fn insert(&mut self, seq_id: SequenceId, seq: Sequence) {
+        self.sequences.insert(seq_id, seq);
+    }
+
+    pub fn remove(&mut self, seq_id: SequenceId) {
+        self.sequences.remove(&seq_id);
+    }
+}