Fix: make prover not certify transactions stored but not certified yet

[jpraynaud]

Content

This PR includes a fix to the Cardano transactions prover to avoid certifying transactions stored in the database, but not already certified. This was causing the error: Proof and certificate don't match when trying to verify this type of transactions instead of marking them as not certified.

Benchmarks

Total Requests	Concurrency	Transactions/Request	Pool (x50) : Request/s	Pool (x50) + Fix not yet certified transactions: Request/s
1000	100	1	273.78	275.95
1000	100	2	201.6	200.65
1000	100	3	143.14	150.64
1000	100	4	115.41	124.02
1000	100	5	91.15	103.31
1000	100	6	80.58	87.72
1000	100	7	74.23	77.33
1000	100	8	65.05	68.08
1000	100	9	58.78	61.77
1000	100	10	52.51	58.13

Running on Linux / 8 cores / 64 GB RAM / 2 TB SSD

Pre-submit checklist

• Branch
  • [x] Tests are provided (if possible)
  • [x] Crates versions are updated (if relevant)
  • [x] Commit sequence broadly makes sense
  • [x] Key commits have useful messages
• PR
  • [x] No clippy warnings in the CI
  • [x] Self-reviewed the diff
  • [x] Useful pull request description
  • [x] Reviewer requested

Issue(s)

Relates to #1719

[github-actions[bot]]

Test Results

    3 files  ±0     43 suites  ±0   8m 38s :stopwatch: -1s 1 013 tests +1  1 013 :white_check_mark: +1  0 :zzz: ±0  0 :x: ±0  1 111 runs  +1  1 111 :white_check_mark: +1  0 :zzz: ±0  0 :x: ±0 

Results for commit 986a3cc2. ± Comparison against base commit ac3eb960.

This pull request removes 2 and adds 3 tests. Note that renamed tests count towards both.

``` mithril-aggregator ‑ services::prover::tests::compute_proof_for_one_set_of_three_known_transactions mithril-aggregator ‑ services::prover::tests::compute_proof_for_one_set_of_three_known_transactions_and_two_unknowns ``` ``` mithril-aggregator ‑ services::prover::tests::cant_compute_proof_for_not_yet_certified_transaction mithril-aggregator ‑ services::prover::tests::compute_proof_for_one_set_of_three_certified_transactions mithril-aggregator ‑ services::prover::tests::compute_proof_for_one_set_of_three_certified_transactions_and_two_unknowns ```

:recycle: This comment has been updated with latest results.