Leak: Trimmed unfoldings are alive through code generation

Fixed in !8807 (closed)

Before:

Slither of IdInfo kept alive (and hence unfoldings etc)

This band is just IdInfo, you can see it stretches over code generation.

Total memory usage during code generation ~400MB

After:

Retained IdInfo, reduced to zero for this particular allocation site

Can see it's not alive over allocation

Approx memory usage during code generation ~300MB.