feat: resolve nested struct members in slither-read-storage

[subashmokshya]

Summary

slither-read-storage did not fully resolve structs nested inside other structs. A nested-struct member (e.g. outer.middle) received a SlotInfo for the nested struct's starting slot, but its own members (outer.middle.inner, outer.middle.inner.a, ...) were never resolved — their elems were left empty, so their slots, sizes, and packing offsets were unavailable.

This PR makes _all_struct_slots recurse into any member that is itself a struct, resolving that member's sub-members relative to the nested struct's base slot, per Solidity's storage-layout rules (a nested struct occupies consecutive slots starting at the parent member's slot). Recursion is depth-agnostic, so arbitrarily deep nesting works.

Root cause

_all_struct_slots iterated only the top-level struct's elems_ordered. When a member's type was itself a Structure, the code computed the member's start slot but never descended into it. The new _all_nested_struct_slots helper reuses the existing _find_struct_var_slot slot arithmetic to resolve each sub-member against the nested struct's base slot, then recurses on any sub-member that is also a struct.

Changes

• slither/tools/read_storage/read_storage.py: recurse into nested struct members in _all_struct_slots; add _all_nested_struct_slots helper.
• tests/unit/tools/read_storage/test_nested_struct.py: new test covering two-level nesting (Outer → Middle → Inner), asserting exact slots for every member, packing offsets for the doubly-nested elementary members, and fully-qualified dotted names.

Test evidence

$ pytest tests/unit/tools/read_storage/ -q
21 passed

The new test fails on master (nested elems empty) and passes with this change. ruff check and ruff format --check are clean on both files.

Fixes #2077

🤖 Generated with Claude Code

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