fix: drop polonius-the-crab, inline unsafe reborrow

[catinspace-au]

polonius-the-crab has so many abandonment issues it needs therapy --
two RustSec advisories across its transitive deps, the whole tree
stagnant for 12+ months. Four crates for a macro that expands to
one line of unsafe.

Inlined the raw-pointer reborrow with a full safety proof and
documentation of every alternative we tried (and why none compiled
without unsafe). Removes 4 crates, clears 2 advisories.

[CLAassistant]

All committers have signed the CLA.

[catinspace-au]

Closing this in favour of a fresh upstreaming approach.

We're consolidating our upstream-targeted work onto a new hyperi-port/* branch chain off current main (0.15.0+). The 0.14 → 0.15 changes (#380, #390, #391, #397, #403) made these original PRs hard to rebase as a unit, and several of them packed too much into a single review. The new chain breaks the work into bite-sized PRs (target <500 LoC, hard limit 1500), each landing as a single squashed commit.

The polonius removal lands first as #422 (already rebased on main, single commit). The remainder of the chain — TCP transport, columnar/Native-format primitive, Inserter RFC #421 implementation, batching, multi-host, etc. — will arrive as separate PRs over the coming weeks. Some pieces (UnifiedClient ergonomic wrapper, DynamicInsert from serde_json::Value) won't be re-proposed upstream and will live in our consumer crate instead.

Sorry for the noise, people.