test: add complex calculation tests with filtered aggregates

[DGollings]

Adds comprehensive tests for calculations that depend on filtered aggregates, including keyset pagination scenarios and SQL fragment calculations with COALESCE patterns. Includes migration for new test fields.

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• Regression tests

[DGollings]

cleaned up

[zachdaniel]

can we format/check credo?

[DGollings]

sure, sorry, although I semi-intentionally ignored the formatting because 'my' mix format does not seem to match 'your' mix format

When I run mix format I'm left with these changes, but did not want to commit more than the files I touched/created

But fixed the whitespace issues

diff --git a/lib/migration_generator/migration_generator.ex b/lib/migration_generator/migration_generator.ex
index 425ccb5..a9d4f43 100644
--- a/lib/migration_generator/migration_generator.ex
+++ b/lib/migration_generator/migration_generator.ex
@@ -494,7 +494,7 @@ defmodule AshPostgres.MigrationGenerator do
                 end)
 
               operations
-              |> organize_operations
+              |> organize_operations()
               |> build_up_and_down()
               |> migration(repo, opts, tenant?, run_without_transaction?)
             end)
diff --git a/test/filter_test.exs b/test/filter_test.exs
index 5492864..d69ab42 100644
--- a/test/filter_test.exs
+++ b/test/filter_test.exs
@@ -1121,13 +1121,13 @@ defmodule AshPostgres.FilterTest do
            |> Ash.Query.for_read(:read)
            |> Ash.Query.filter(first_member.id != ^cm2.id)
            |> Ash.read!()
-           |> length == 4
+           |> length() == 4
 
     assert Channel
            |> Ash.Query.for_read(:read)
            |> Ash.Query.filter(first_member.id == ^cm2.id)
            |> Ash.read!()
-           |> length == 1
+           |> length() == 1
   end
 
   test "using exists with from_many?" do
@@ -1142,13 +1142,13 @@ defmodule AshPostgres.FilterTest do
            |> Ash.Query.for_read(:read)
            |> Ash.Query.filter(exists(first_member, id == ^cm2.id))
            |> Ash.read!()
-           |> length == 0
+           |> length() == 0
 
     assert Channel
            |> Ash.Query.for_read(:read)
            |> Ash.Query.filter(exists(first_member, id == ^cm1.id))
            |> Ash.read!()
-           |> length == 1
+           |> length() == 1
   end
 
   test "using `(is_nil(relationship) and other_relation_filter)` will trigger left join" do