[IMP] selection_stream: add unobserve method

The selection stream processor was missing a method to stop observing
events after starting to observe them, which could lead to memory leak.

The `AggregateStatisticsStore` was never releasing its observation,
which was not a problem in practice because the store is never disposed,
but let's fix it anyway.

Task: 3149088
Part-of: #7241
Signed-off-by: Pierre Rousseau (pro) <pro@odoo.com>

Author: hokolomopo

packages/o-spreadsheet-engine/src/selection_stream/event_stream.ts

@@ -65,6 +65,10 @@ export class EventStream<Event> {
     this.observers.set(owner, { owner, callbacks });
   }
 
+  unobserve(owner: Owner) {
+    this.observers.delete(owner);
+  }
+
   /**
    * Capture the stream for yourself
    */

packages/o-spreadsheet-engine/src/selection_stream/selection_stream_processor.ts

@@ -77,6 +77,10 @@ export class SelectionStreamProcessorImpl implements SelectionStreamProcessor {
     this.stream.observe(owner, callbacks);
   }
 
+  unobserve(owner: unknown) {
+    this.stream.unobserve(owner);
+  }
+
   release(owner: unknown) {
     if (this.stream.isListening(owner)) {
       this.stream.release(owner);

packages/o-spreadsheet-engine/src/types/selection_stream_processor.ts

@@ -9,6 +9,7 @@ type StatefulStream<Event, State> = {
   resetDefaultAnchor: (owner: unknown, state: State) => void;
   resetAnchor: (owner: unknown, state: State) => void;
   observe: (owner: unknown, callbacks: StreamCallbacks<Event>) => void;
+  unobserve: (owner: unknown) => void;
   release: (owner: unknown) => void;
   getBackToDefault(): void;
 };

src/components/bottom_bar/bottom_bar_statistic/aggregate_statistics_store.ts

@@ -71,6 +71,9 @@ export class AggregateStatisticsStore extends SpreadsheetStore {
     this.model.selection.observe(this, {
       handleEvent: this.handleEvent.bind(this),
     });
+    this.onDispose(() => {
+      this.model.selection.unobserve(this);
+    });
   }
 
   handle(cmd: Command) {