Fix static analysis issues for dart 3.6

[ntkme]

This PR fixes the following issues showing up with today's dart 3.6 release:

warning • lib/src/embedded/compilation_dispatcher.dart:94:11 • This default clause is covered by the previous cases. Try removing the default clause, or restructuring the preceding patterns. • unreachable_switch_default
   info • lib/src/callable/built_in.dart:112:35 • Statements in an if should be enclosed in a block. Try wrapping the statement in a block. • curly_braces_in_flow_control_structures