Reduce whitespace in jinja2 templates

Omit extra newlines when combining and including templates.

Adjust the xfer/ns8/small.db.j2 so it doesn't trim the endline twice
(as that would join the two subsequent records on the same line).

bin/tests/system/isctest/template.py

@@ -44,6 +44,8 @@ class TemplateEngine:
             undefined=jinja2.StrictUndefined,
             variable_start_string="@",
             variable_end_string="@",
+            trim_blocks=True,
+            keep_trailing_newline=True,
         )
         # allow instantiating the template dataclasses in jinja2 templates when
         # using {% set %}

bin/tests/system/xfer/ns8/small.db.j2

@@ -1,4 +1,4 @@
 {% for i in range(4096) %}
 name@i@ 259200 A 1.2.3.4
 name@i@ 259200 TXT "Hello World @i@"
-{%- endfor %}
+{% endfor %}