bench/lang: simplify signature of the test function

Signed-off-by: Jean Privat <jean@pryen.org>
bench/lang: add bench_base

Signed-off-by: Jean Privat <jean@pryen.org>
bench/lang: force covariance in scala&csharp

Signed-off-by: Jean Privat <jean@pryen.org>
bench: add covar/depthnot and fts_nesting

Signed-off-by: Jean Privat <jean@pryen.org>