Add a poll-based tracker policy worker that claims banners flagged for
policy generation, clears the flag, and rebuilds the cookie and
tracking technologies policy from the latest published snapshot. A
banner that lost its published version is skipped rather than failed.
Wire the worker into probod with crash propagation and graceful
shutdown alongside the other tracker workers.
Signed-off-by: Émile Ré <emile@probo.com>
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