[FIX] web: fix calendar's sidebar spacings

The datetime picker's top and bottom padding is unnecessary in the 
calendar's sidebar.
An extra margin is added below the filters because the sync buttons
were too close.

task-3570053

Part-of: odoo/odoo#139736

addons/web/static/src/core/datetime/datetime_picker.xml

@@ -136,7 +136,8 @@
 
     <t t-name="web.DateTimePicker">
         <div
-            class="o_datetime_picker d-flex flex-column gap-2 p-2 p-lg-3 user-select-none"
+            class="o_datetime_picker d-flex flex-column gap-2 user-select-none"
+            t-att-class="!isLastPrecisionLevel ? 'p-2 p-lg-3' : ''"
             t-attf-style="--DateTimePicker__Day-template-columns: {{ props.showWeekNumbers ?? !props.range ? 8 : 7 }}"
         >
             <nav class="o_datetime_picker_header btn-group">

addons/web/static/src/views/calendar/filter_panel/calendar_filter_panel.xml

@@ -5,7 +5,7 @@
         <t t-foreach="props.model.filterSections" t-as="section" t-key="section.fieldName">
             <t t-if="section.filters.length gt 0">
                 <div
-                    class="o_calendar_filter d-flex flex-column gap-1 mt-4"
+                    class="o_calendar_filter d-flex flex-column gap-1 mt-4 mb-2"
                     t-att-class="{'o-calendar-filter-panel--section-collapsed': isSectionCollapsed(section)}"
                     t-att-data-name="section.fieldName"
                 >