v0.16.1

Update version to 0.16.1 (#2145)

Welcome to pgrx v0.16.1. This is a relatively minor release but does add
support for Postgres v18, released on September 25, 2025.

As always, install/update `cargo-pgrx` with `cargo install cargo-pgrx
--version 0.16.1 --locked`. Then run `cargo pgrx update` in all your
extension crates.

To pick up Postgres v18, you'll need to run (at least) `cargo pgrx init`
and then add the `pg18` feature flag to your extension's `Cargo.toml`.


## What's Changed

* remove polyfill crates by @usamoi in
https://github.com/pgcentralfoundation/pgrx/pull/2128
* Example : register PostgreSQL hooks by @daamien in
https://github.com/pgcentralfoundation/pgrx/pull/2125
* add more WAL/replication headers by @eeeebbbbrrrr in
https://github.com/pgcentralfoundation/pgrx/pull/2130
* remove home, supports-color 0.2 and update toml, color-eyre by @usamoi
in https://github.com/pgcentralfoundation/pgrx/pull/2133
* cargo-pgrx: fix pg_regress path inconsistency by @charmitro in
https://github.com/pgcentralfoundation/pgrx/pull/2137
* fix big endian by @usamoi in
https://github.com/pgcentralfoundation/pgrx/pull/2132
* Fixing CI by @eeeebbbbrrrr in
https://github.com/pgcentralfoundation/pgrx/pull/2143
* pg18 support by @eeeebbbbrrrr in
https://github.com/pgcentralfoundation/pgrx/pull/2144


**Full Changelog**:
https://github.com/pgcentralfoundation/pgrx/compare/v0.16.0...v0.16.1