Precision of DateTime fields, when specified, do not match the DB schema

Description

When an object is created by FactoryBot, and a value with a greater precision than permitted by the DB schema is specified for one of its DateTime fields, the value for that field does not reflect the precision specified by the DB schema until the record is reloaded.

Reproduction Steps

Specs to reproduce:

describe 'FactoryBot' do
  context 'when a DateTime field is specified with greater precision than allowed by the DB' do
    let(:nanosecond_precision_datetime) { DateTime.parse("2025-01-01T11:11:11.123456789") }
    let(:microsecond_precision_datetime) { DateTime.parse("2025-01-01T11:11:11.123456") }
    let(:identity) { create(:identity, updated_at: nanosecond_precision_datetime) }

    it 'does not truncate the DateTime to the DB precision until the record is reloaded' do
      expect(identity.updated_at).to eq(nanosecond_precision_datetime)
      identity.reload
      expect(identity.updated_at).to eq(microsecond_precision_datetime)
    end
  end

  context "when a DateTime field's value is generated by FactoryBot / ActiveRecord" do
    let(:identity) { create(:identity) }

    it 'returns the same value both before and after reloading the record' do
      updated_at_before_reload = identity.updated_at
      expect(identity.updated_at).to eq(updated_at_before_reload)
      identity.reload
      expect(identity.updated_at).to eq(updated_at_before_reload)
    end
  end
end

Relevant part of the DB schema:

ActiveRecord::Schema[7.0].define do
  create_table "identities", id: { type: :string, limit: 12 }, force: :cascade do |t|
     t.datetime "updated_at", precision: nil, null: false

Expected behavior

The value for updated_at in the first spec should be at microsecond precision both before and after reloading.

Actual behavior

Calling reload on the record changed the value of the updated_at field.

System configuration

factory_bot version: 6.2.0
rails version: 7.0.8.6
ruby version: 3.3.4

Start by running the provided reproduction specs with the stated FactoryBot, Rails, and Ruby versions, then trace the record creation and reload behavior for the identity's updated_at field. Done means an explicitly over-precise value is truncated to database precision before observation, while FactoryBot/ActiveRecord-generated timestamps remain unchanged across reloads.