Summary

• Replace assert() with explicit if/throw in getInt(), getDouble(), and getBool() so null-safety checks work in release builds (fixes AssertionError - Missing VAR-NAME #136)
• Error messages now include the variable name for easier debugging
• Aligns typed getters with get(), which already uses explicit throws

Problem

Dart strips assert() in release builds. When a variable was missing and no fallback was provided, release builds threw an opaque Null check operator used on a null value instead of a helpful error message.

Note on release-build behavior

In release mode, the thrown exception type changes from TypeError (accidental, from fallback!) to AssertionError (intentional, matching debug mode). If your release code catches on TypeError around these methods, update to on AssertionError or on Error.

Test plan

• Existing throwsAssertionError tests continue to pass
• New test verifies error messages contain the variable name
• All 37 tests pass