Free inactive shape resources to reduce memory usage

We've recently started loading shapes lazily #3243 to avoid a thundering shape creation during boot, to have quicker boot times and more sustainable resource usage growth.

Now, we want to explore freeing shape resources after a period of inactivity. The idea is that this reduces memory usage by maintaining only active shape processes (bounded by shape cache size).
Trade-off: requires opening/closing file handlers during shape matching, which is a critical path operation. This experiment should be evaluated before pursuing pooled shape consumers or other alternatives, as they would have to still manage file handlers.