Bump mockito to 0.31.1

[Pi-Cla]

Fixes a RUSTSEC advisory where mockito was depending on an unmaintained crate
lipanski/mockito#145

[Pi-Cla]

Bumping it further requires us to rewrite some stuff due to breaking changes (whereas I mainly just want to make sure we are not depending on any unmaintained crates)

[lpil]

Hello! I think this doesn't upgrade mockito, the upper bound is the same before and after this commit.

https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html

[Pi-Cla]

Hello! I think this doesn't upgrade mockito, the upper bound is the same before and after this commit.

https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html

Looking at cargo reference you linked it lists this:

0.2    :=  >=0.2.0, <0.3.0

mockito is a v0 package so a dependency on 0.30.0 means it can not be increased to 0.31.1.
The dependency currently is:

0.30    :=  >=0.30.0, <0.31.0

This will bump it up to:

0.31.1    :=  >=0.31.1, <0.32.0

[lpil]

Ah! I missed the v0 bit. Thank you for explaining that to me