Restore secondary_index test

[ptagl]

Overview

This commit removed a test to check the management of secondary keys in smart contract tables.
The test was initially meant to test a specific scenario: the SNARKtor Testnet contract compiled to WASM.
The problem is that WASM contracts (compiled using rscdk) treat the Checksum256 with a different encoding compared to the C++ compiler.

For this reason, antelope-rs has been made compatible with the C++ encoding and the test has been removed.

The test should be added again once the issue has been solved. This may require a fork of the rscdk to fix the encoding mentioned above, and a new deployment of the SNARKtor contract(s).

Links

• Commit that removed the test: 598dd54
• Revert commit that fixed the Checksum256 encoding to be compatible with C++ smart contracts (and not with WASM contracts anymore): 02d0e7e
• Initial commit that introduced the Checksum256 encoding compatible with WASM smart contracts (but not with C++ ones): 6977b8b

Acceptance Criteria

• A secondary_index test is available again in the codebase
• The test passes