fix(explore): Reset aggregate cursor on filter changes (#120200)

When Explore's shared query-params context applies a new filter, it
already marks both pagination cursors for reset. The spans URL writer
handled the samples cursor but ignored `aggregateCursor`, leaving
aggregate mode on a stale page and potentially showing an empty result
set.

This change writes the aggregate cursor through the same nullable URL
helper, so a query change removes it and returns aggregate results to
page one. It also adds regression coverage for clearing a populated
aggregate cursor while applying a filter.

Closes EXP-1111

---------

Co-authored-by: sentry-junior[bot] <264270552+sentry-junior[bot]@users.noreply.github.com>
Co-authored-by: Nicholas Deschenes <nicholas.deschenes@sentry.io>

Author: sentry-junior[bot]

static/app/views/explore/spans/spansQueryParams.spec.tsx

@@ -404,6 +404,20 @@ describe('getReadableQueryParamsFromLocation', () => {
 });
 
 describe('getTargetWithReadableQueryParams', () => {
+  it('removes the aggregate cursor when it is reset', () => {
+    const location = locationFixture({aggregateCursor: '0:50:0'});
+
+    const initialTarget = getTargetWithReadableQueryParams(location, {});
+    expect(initialTarget.query).toEqual({aggregateCursor: '0:50:0'});
+
+    const target = getTargetWithReadableQueryParams(location, {
+      aggregateCursor: null,
+      query: 'span.name:checkout',
+    });
+
+    expect(target.query).toEqual({query: 'span.name:checkout'});
+  });
+
   it('writes breakdown query params', () => {
     const location = locationFixture({});
     const target = getTargetWithReadableQueryParams(location, {

static/app/views/explore/spans/spansQueryParams.tsx

@@ -150,6 +150,11 @@ export function getTargetWithReadableQueryParams(
         )
   );
 
+  updateNullableLocation(
+    target,
+    SPANS_AGGREGATE_CURSOR,
+    writableQueryParams.aggregateCursor
+  );
   updateNullableLocation(
     target,
     SPANS_AGGREGATE_FIELD_KEY,