Tests write a literal `:memory:` directory into the repo root

[eldonm]

:memory: is a SQLite sentinel. JsonDB has no such concept, so when it is handed that string as a db_path it does the only thing it can: creates a literal directory named :memory: and writes to it.

That directory lands in the repo root, untracked, and persists after the run:

:memory:/node/n.Root.root.json

Where

tests/api/decorators/test_deferred_registry.py builds its server config with:

database=DatabaseConfig(db_type="json", db_path=":memory:")

...at lines 119, 162, 177, 197, 212, 239, 272, 299.

Why it matters

Two separate problems:

1. Test isolation. The suite writes into the working directory and leaves the artifact behind. Anyone running pytest locally accumulates a :memory: directory in their checkout, and git status grows a permanent untracked entry that is easy to git add -A by accident.
2. The tests are not testing what they intend. They are asking for an ephemeral in-memory database and silently getting a persistent on-disk one. State survives within a run, and across runs, in a way the author plainly did not intend.

Repro

git status --short          # clean
pytest tests/api/decorators/test_deferred_registry.py -q
git status --short          # ?? :memory:/

Suggested fix

Use tmp_path for the json path, which is what the tests actually want:

database=DatabaseConfig(db_type="json", db_path=str(tmp_path / "jvdb"))

Worth considering separately: JsonDB could reject ":memory:" outright rather than creating a strangely-named directory. Silently interpreting a sentinel from another backend as a relative path is the part that made this invisible.

Found while running the full suite during #37 / #38.