feat: add detector for complex struct getters with omitted members

[ep0chzer0]

Summary

Adds a new informational detector (complex-struct-getter) that identifies public state variables containing structs where the automatic getter omits array and mapping members.

Closes #2779

Problem

Solidity's auto-generated getters for public struct variables silently skip array and mapping members. This can cause confusion about data accessibility and lead to integration issues:

struct UserData {
    string name;           // ✓ Returned by getter
    uint256 balance;       // ✓ Returned by getter
    uint256[] tokenIds;    // ✗ Omitted
    mapping(address => uint256) allowances; // ✗ Omitted
}

UserData public userData; // Getter won't return tokenIds or allowances

Detection Logic

• Iterates public state variables with struct types
• Identifies array and mapping members omitted from the getter
• Recursively checks nested structs for deeply omitted members
• Handles recursive struct types safely (prevents infinite loops)
• Reports all omitted members with their types

Test Coverage

7 contracts covering:

• DirectArrayMapping — struct with both arrays and mappings (flagged)
• NestedStruct — nested struct containing an array (flagged)
• MappingOnly — struct with only a mapping (flagged)
• SimpleStruct — struct with only elementary types (NOT flagged)
• PrivateComplex — complex struct but internal visibility (NOT flagged)
• NoStruct — plain state variables, no structs (NOT flagged)
• NestedSimple — nested struct with only elementary types (NOT flagged)

Files Changed

• slither/detectors/variables/complex_struct_getter.py — New detector
• slither/detectors/all_detectors.py — Register detector
• tests/e2e/detectors/test_detectors.py — Add test entry
• tests/e2e/detectors/test_data/complex-struct-getter/ — Test contract and artifact
• tests/e2e/detectors/snapshots/ — Expected output snapshot

All 382 detector tests pass (381 existing + 1 new).