Fix TypeError when dumping events containing bytes as JSON

[ZayanKhan-12]

Fixes #91

Problem

On Python 3 the decoders produce bytes for blob/string fields, and compat.json_dumps passes the event straight to json.dumps, which raises:

TypeError: Object of type bytes is not JSON serializable

for any command that hits such an event — e.g. python -m heroprotocol --initdata --json <replay>, as reported (and reproduced here with a bytes-containing event before the fix).

Fix

json_dumps now recursively decodes bytes — including dict keys, and values nested in lists/tuples — using the encoding argument it already receives, which is exactly what json.dumps(obj, encoding=...) did on Python 2, so Python 3 output matches the legacy behavior. The iso-8859-1 encoding the CLI passes decodes every possible byte value, so the conversion never raises.

Verification

• Before the fix: json_dumps({'m_name': b'Alarak'}, encoding='iso-8859-1') reproduces the exact TypeError from the issue
• New tests/test_compat.py (pytest, 2 tests) covers bytes values, bytes dict keys, nesting in lists/tuples, and all 256 byte values round-tripping
• CI checks run locally on the changed files: black -S --check clean, codespell clean, flake8 --select=E9,F63,F7,F82 clean

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