Array index reset

[davekeeshan]

Summary

I raised this as a possibility in the comment thread of #51, but there was no feedback, I figured I open a PR so we can address it properly. I have made this change locally and it is working for my team

Adds limited support for heterogeneous instance arrays via indexed dynamic property assignments (DPAs), addressing the use case in #51 Support for heterogeneous-arrays.:

Example:

GPIO_INSTANCE GPIO[4];
GPIO[0].CFG.CFG->reset = CFG_DEFAULT_3;
GPIO[3].CFG.CFG->reset = gpio_enum::PLL_BYPASS;

Support is intentionally limited to the reset property only. Other properties, array sub-ranges, and references that index more than one array in the same path remain unsupported.

Implementation

Indexed DPAs that target a single array element create a per-element component override in AddressableComponent.array_element_overrides. Elements without an override continue to share the array's component tree, preserving structural identity (size, addressing, field layout).

• Parse/elaborate: resolve array indices and create element overrides; defer bounds checking when array dimensions are not yet known (parameterized arrays)
• Elaboration: evaluate expressions, sync structure/addresses (including nested reg arrays), and propagate array metadata to overrides
• Validation: validate override subtrees so invalid reset values are rejected consistently with whole-array assignments
• Node API: consistent is_array, addressing, and path behaviour for unrolled elements; extended DPA type names on override subtrees (e.g. CFG_reset_b vs CFG_reset_a)
• DPA ordering: propagate subsequent whole-array DPAs into existing element overrides

Limitations

• Only reset may be assigned via an indexed DPA reference
• Only one array index per reference path (e.g. rf[0].r1[1].f->reset is rejected)
• Array sub-ranges (my_inst[1:4]) are not supported

Documentation

Updates docs/known_issues.rst and docs/dev_notes/instance_arrays.rst to describe the supported subset and internal representation.

Test plan

• test/test_dpas.py — indexed reset on regfile arrays, reg arrays, parameterized dimensions, whole-array DPA propagation, type-name differentiation, array API consistency
• Error cases: non-reset property, OOB index, multi-array path, dimension mismatch, invalid reset width

Partially addresses #51 (reset-only heterogeneous arrays).