Add arbitrary base math log (#7409)

Adds new command `math log` that takes as a required positional argument
a base.

Specialized for `math log 2` and `math log 10` for better performance
and precision that matches the expectations there. This leads to
discontinuities in numerical error but should make a better trade-off
for common usecases.


Example testing of the happy path

crates/nu-command/src/default_context.rs

@@ -422,6 +422,7 @@ pub fn create_default_context() -> EngineState {
             MathTau,
             MathEuler,
             MathLn,
+            MathLog,
         };
 
         // Network