feat(core): add timestamp check

[mariocao]

Motivation

To enhance the security and integrity of the SEDA protocol, we need to ensure that results cannot be posted with timestamps that precede their corresponding requests. This validation prevents potential temporal inconsistencies in the DR (Data Request) lifecycle.

Explanation of Changes

The changes introduce timestamp validation in the SedaCoreV1 contract:

1. Added a new error type InvalidResultTimestamp for cases where result timestamps precede request timestamps
2. Extended the storage layout with a requestTimestamps mapping to track timestamps of pending requests
3. Modified postRequest to store the request timestamp
4. Enhanced postResult to:
   • Validate that result timestamps are after request timestamps
   • Clean up the timestamp storage when processing results
   • Revert with InvalidResultTimestamp if validation fails

Important

The implementation allows for backwards compatibility by not enforcing validation for requests not tracked by this contract (where requestTimestamp = 0). Is this what we want?

Testing

Added new test cases in test/core/SedaCoreV1.test.ts:

1. Modified the test fixtures to include an edge case with an invalid timestamp (set to 1 unix timestamp - 1970-01-01T00:00:01Z)
2. Added a new test case should reject results with invalid timestamps that:
   • Posts a request
   • Attempts to post a result with a timestamp from 1970
   • Verifies that the transaction reverts with InvalidResultTimestamp error

Related PRs and Issues

• Closes ✨ Add “result timestamp window” to core contract #66

[Thomasvdam]

The implementation allows for backwards compatibility by not enforcing validation for requests not tracked by this contract (where requestTimestamp = 0). Is this what we want?

This makes sense to me for our reference implementation. If people want to add additional 'freshness' constraints they can implement that in their own core contract or another contract in between.