TestCase::routing_bug_minimal reproduces the per-path routing bug fixed
by commits 1e0fefd, 306a31b, 5577902 in NomtVerifierStorage. It is
a two-round TestCase with two kernel writes per round (and zero user
writes), bisected from captured StateAccesses of the slow
demo-rollup test_mock_proof_public_data_matches_witnesses down to the
minimal input that still makes the pre-fix verifier's
verify_multi_proof_update diverge from session.finish().root().

Other additions:
- Four additional multi-write/multi-round TestCases for general coverage
  (multi_write_distinct_keys, multi_write_both_namespaces_distinct,
  mixed_reads_and_multi_writes, multi_round_multi_write). They don't
  trigger the routing bug on their own, but exercise code paths the
  single-write cases didn't.
- serde::Serialize / serde::Deserialize derives on StateAccesses and
  OrderedReadsAndWrites in sov-state::cache, gated behind the
  test-utils feature.
- dump_state_accesses_if_enabled in NomtProverStorage (gated behind
  test-utils + the SOV_DUMP_STATE_ACCESSES=<dir> env var) for capturing
  real STF state accesses as JSON. This is how routing_bug_minimal was
  derived.
- serde_json added as optional test-utils-only dep on sov-state.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Restores zk_storage.rs and prover_storage.rs to their origin/dev state,
undoing the aggregated effect of the three fix commits on these two
files. Other changes from those commits (outside these two files) are
not present in this branch's ancestry anyway.

The dump_state_accesses_if_enabled helper added in the previous commit
lived in prover_storage.rs and is wiped by this revert; that is
acceptable for this branch because the captures it produced are already
inlined into TestCase::routing_bug_minimal.

After this commit, running
  cargo nextest run -p sov-modules-api state_tests::compute_state_update
is expected to FAIL: test_roundtrip_nomt panics with a StorageRoot
mismatch on the kernel half of routing_bug_minimal, demonstrating the
per-path routing divergence between NomtProverStorage (NOMT
session.finish) and NomtVerifierStorage (verify_multi_proof_update on a
flat update list).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>