build: fix caller-utils spoiling fresh builds of repo

[nick1udwig]

Problem

When building, we modify Cargo.toml to include caller-utils (the machine-generated dependencies).
However, if this is committed to the repo where whatever hyperapp lives, it means that fresh clones will fail to build (since the machine-generated code does not exist!).

Solution

Slightly modify:

1. Make the dependency optional
2. Make the workspace member a glob -- which is "optional"

Docs Update

None

Notes

None

[nick1udwig]

#329