* Fixes a rather egregious bug with respect to the inability to return arbitrary objects from py::init (was causing aliasing of multiple py::object -> native instance).
* Makes Modules and Operations referencable types so that they can be reliably depended on.
* Uniques python operation instances within a context. Opens the door for further accounting.
* Next I will retrofit region and block to be dependent on the operation, and I will attempt to model the API to avoid detached regions/blocks, which will simplify things a lot (in that world, only operations can be detached).
* Added quite a bit of test coverage to check for leaks and reference issues.
* Supercedes: https://reviews.llvm.org/D87213
Differential Revision: https://reviews.llvm.org/D87958
* Generic mlir.ir.Attribute class.
* First standard attribute (mlir.ir.StringAttr), following the same pattern as generic vs standard types.
* NamedAttribute class.
Differential Revision: https://reviews.llvm.org/D86250
Stella Laurenzo