The deterministic tracker-mapping heuristics group patterns by shared
initiator domain, but tag managers, customer-data platforms, and
generic CDNs (Google Tag Manager, Segment, cloudfront.net, ...)
initiate trackers for many unrelated vendors. Grouping on such a
domain mis-attributes one vendor's tracker to another.
Add uri.FilterSharedInfrastructureDomains backed by a curated eTLD+1
denylist and apply it once in resolveDeterministic, so sibling
grouping, catalog domain matching, and the sibling re-enqueue cascade
all ignore shared-infrastructure hosts. Vendor-specific domains such
as google-analytics.com are intentionally kept as a same-vendor
signal. The agent path is unchanged: it still sees observed domains,
now with a prompt caveat about shared infrastructure.
Update the two sibling tests that used googletagmanager.com as the
initiator domain to a vendor domain, since that host is now stripped
before grouping.
Signed-off-by: Émile Ré <emile@probo.com>