feat: add UInt128 type support for PostgreSQL to ClickHouse replication

[testtt234]

When PostgreSQL has a uint128 extension (pg_uint128), PeerDB now recognizes the type and maps it natively to ClickHouse's UInt128 instead of falling back to string. Adds full pipeline support: type enum, QValue struct, Avro serialization (16-byte fixed), CDC handling, and connector mappings.

[CLAassistant]

All committers have signed the CLA.

[ilidemi]

We aim to support the most popular extensions (like pgvector) but pg_uint128 would be below that bar. Given it does propagate as a string and ClickHouse supports arbitrary transformations in MVs, we'd direct people to follow that route (or use a fork).

[testtt234]

but, it's literally just 90 lines of code

[testtt234]

It's not about supporting postgres extension.
it's about supporting postgres column type

just because conversion to string doens't break the replication, it doens't mean it doens't break the applications.

please

[testtt234]

It doesn't even make sense business wise, just because an extension is popular it doesn't mean enterprise businesses would use it.
or just because an extension isn't popular that enterprise would not use it.

pg-uint128 is type of extension only enterprise and deep tech startups would ever use, it is an edge case for you guys, to support broader spectrum of deep tech startups