Not depend on serde

[iquerejeta]

Removed panics from from_bytes() functions, and removed dependency on SERDE. Now the code uses from/to_bytes instead. Trying to figure out if this solves the problem.

[github-actions]

Unit Test Results

    5 files  ±  0    14 suites  +3   2m 51s ⏱️ +25s
166 tests +72  166 ✔️ +72  0 💤 ±0  0 ❌ ±0 

Results for commit f06bb4b. ± Comparison against base commit d011bbb.

This pull request removes 1 and adds 73 tests. Note that renamed tests count towards both.

src/stm.rs - stm::StmSigner<D> ‑ new_epoch (line 678)

beacon_store::tests ‑ test_can_store_beacon
beacon_store::tests ‑ test_reset_current_beacon_ok
certificate_store::certificate_store::test ‑ get_certificate_with_good_hash
certificate_store::certificate_store::test ‑ get_certificate_with_wrong_hash
certificate_store::certificate_store::test ‑ list_has_some_members
certificate_store::certificate_store::test ‑ list_is_empty
certificate_store::certificate_store::test ‑ save_certificate_once
certificate_store::certificate_store::test ‑ update_certificate
certificate_store::dumb_adapter::tests ‑ test_list_with_last_zero
certificate_store::dumb_adapter::tests ‑ test_list_with_no_record
…

♻️ This comment has been updated with latest results.

[iquerejeta]

Moved to #236 for testing #207 . I'm closing this.