Mithril Client uses real digest

[jpraynaud]

The Mithril Client is able to:

• Retrieve the certificate associated to a snapshot from the Mithril Aggregator
• Compute the digest of the downloaded snapshot archive
• Verify the computed digest matches with the certificate digest
• Verify the hash of the certificate is valid
• Verify the validity of the multi signature in the certificate

Closes #180

[github-actions]

Unit Test Results

    5 files  ±0    14 suites  ±0   2m 13s ⏱️ -18s
140 tests +6  140 ✔️ +6  0 💤 ±0  0 ❌ ±0 

Results for commit ae10e2c. ± Comparison against base commit 0be8dd1.

This pull request removes 6 and adds 12 tests. Note that renamed tests count towards both.

client::tests ‑ test_list_snapshots_ko
client::tests ‑ test_list_snapshots_ok
client::tests ‑ test_restore_snapshot_ok
client::tests ‑ test_restore_unpack_snapshot
client::tests ‑ test_show_snapshot_ko
client::tests ‑ test_show_snapshot_ok

runtime::tests ‑ test_list_snapshots_ko
runtime::tests ‑ test_list_snapshots_ok
runtime::tests ‑ test_restore_snapshot_ko_certificate_hash_not_matching
runtime::tests ‑ test_restore_snapshot_ko_digester_error
runtime::tests ‑ test_restore_snapshot_ko_digests_not_matching
runtime::tests ‑ test_restore_snapshot_ko_get_certificate_details
runtime::tests ‑ test_restore_snapshot_ko_get_snapshot_details
runtime::tests ‑ test_restore_snapshot_ko_restore_unpack_snapshot
runtime::tests ‑ test_restore_snapshot_ko_verify_multi_signature
runtime::tests ‑ test_restore_snapshot_ok
…

♻️ This comment has been updated with latest results.