Bug: Memory grows on repeated runs, with instance re-use

[dphilla]

For reference/reproduce

[dphilla]

cc: @pojntfx

Fixed with new API for clearing active Instances/Modules.

runtime.Clear() removes all active instances from an instantiated runtime.

see: #130

This is especially important for the mentioned use-case, where, during a long-running process, repeated invocation of the same function or instance (rather than chaining different functions) causes the runtime to instantiate and manage many of the same Wasm/Scale function instances via the underlying Wasm runtime (Wazero). Now those can be managed by the user at a per-runtime level :)