db-analyser: avoid partial trace-ledger era-transition path

[dancewithheart]

Addresses #48 by

return Maybe a from analyseWithLedgerState and emit no traces on era transitions

so tracing is skipped at the boundary instead of crashing.

I was not able to reproduce the db-analyser --trace-ledger crash in tests.
I added an integration-style test that runs TraceLedgerProcessing on
synthesized Cardano test data and checks that analysis completes without
throwing.

Feedback would be very welcome: whether this is the right direction, and what
the best approach would be for a regression test.

[dancewithheart]

The failing storage-test: ChainDB q-s-m.sequential, on CI with message

PostconditionFailed real response didn't match model response
IteratorResultGCed {real = True, iterResult = IteratorResult}
:/=
IteratorResultGCed {real = False, iterResult = IteratorExhausted}

can be reproduced on main branch with:

cabal test storage-test --test-options='-p "ouroboros-storage.Storage.ChainDB.ChainDB q-s-m.sequential" --quickcheck-replay="(SMGen 1310011906619349515 3290980239361589411,61)"'

it seems it is reported as #299. So this one looks unrelated to the change in this PR.

[dancewithheart]

The failing byron-test with Node CoreId (CoreNodeId 0)'s ImmutableDB is leaking file handles on CI also reproduces on main:

cabal test byron-test --test-options='-p "Byron.simple convergence" --quickcheck-replay="(SMGen 13964393832207003311 14774351647257379649,80)"'

So this also looks unrelated to this PR.

Possibly related to #1294.

[dancewithheart]

Converted to draft - probably without reproducing error manually and in tests the change is not that useful.