test(util): cover command stream line delivery and EOF flushing

Add focused coverage for the new GLib command stream helper.

These tests verify that complete lines are emitted as they arrive and that EOF flushes a final unterminated line without duplicating a newline-terminated one.

That behavior is the contract the custom module will rely on when its continuous command handling moves onto this helper.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

test/utils/meson.build

@@ -15,8 +15,10 @@ test_src = files(
     'SafeSignal.cpp',
     'sleeper_thread.cpp',
     'command.cpp',
+    'command_line_stream.cpp',
     'css_reload_helper.cpp',
     '../../src/util/css_reload_helper.cpp',
+    '../../src/util/command_line_stream.cpp',
 )
 
 if tz_dep.found()