Add multiplication to expressions

[jinmannwong]

Description

• New class Mul in expressions
• New class BinMatOp, where composition of math operations is allowed
• Define __mul__ for RepeatString, RepeatEnumerated and RepeatInteger

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[jinmannwong]

I noticed that __div__ is defined Overloaded, is there a reason that __mul__ wasn't? I have only added it to some specific attributes here, where I think the operation makes sense.

[colonesej]

I agree with just adding to where it makes sense. I scanned around and could not see why __mul__ is a overload. Is the division symbol anyhow meaningful for ecflow in any context? like

expr1 / expr2

would this be interpreted as a Path-like operation?

[jinmannwong]

Ah, I see, this could be the case.

[jinmannwong]

@corentincarton, please can this be merged when you have time, if you are ok with the changes