test(lua): add tests for format object

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(lua): typos and a bug in the expr Lua bindings

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(lua): add tests for expr object

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(lua): add tests for expr object