test(#492): add assert_supply_equals_holder_sum helper with 3 test cases

[BWM0223]

Fixes #492

Summary

Adds assert_supply_equals_holder_sum helper to creator-keys/tests/supply_holder_sum_helper.rs matching the existing test module pattern.

Implementation

pub fn assert_supply_equals_holder_sum(
    client: &ContractClient,
    creator_id: &Address,
    holders: &[Address],
)

• Reads get_total_key_supply and sums get_key_balance for each holder
• Panics with descriptive message showing both total_supply and computed sum

Tests (3)

• helper_passes_on_fresh_state — 0 supply, 0 holders, no panic
• helper_detects_supply_mismatch — verifies panic on mismatch
• helper_passes_when_supply_matches_holders — equal values, no panic

Payment: ETH 0xeaCAb48a4bfA0CED0e668c166615927115655594

[BWM0223]

Implementation complete and ready for review. Payment wallets ready: ETH 0xeaCAb48a4bfA0CED0e668c166615927115655594 | SOL C3MD2yfWYebB8FYXpq6ooqzU5GCQB1bDxbDhQf1JfiCW | BTC bc1qtmlgtvg7xgv0zry3ct90elp3y7d3ffdutk4e2f