Add serialized tsvector search pushdown

[k-bx]

Summary

• recognize compatibility views that expose ClickHouse String columns with tsvectorin(text::cstring)
• deparse constant tsvector @@ tsquery predicates as ClickHouse RE2/array predicates
• support exact and prefix operands, boolean operators, positional phrases, reverse @@, NULLs, and stripped vectors
• leave weighted and non-constant queries for local PostgreSQL evaluation

Motivation

CDC and compatibility layers often serialize PostgreSQL tsvector values into ClickHouse strings. PostgreSQL currently has to retrieve every serialized value and apply @@ locally, which defeats predicate pushdown for full-text search.

Tests

• full PostgreSQL 18 regression suite against ClickHouse 26.3.12.3 (39/39)
• PostgreSQL 14 compile
• upstream pre-commit suite
• new parity coverage for Russian lexemes, numeric lexemes vs position numbers, prefixes, boolean queries, phrases/distances, reverse @@, NULLs, stripped vectors, weighted-query fallback, and custom/generic prepared plans

[theory]

Looks useful, but I think you need to run git submodule update --init --recursive to get the latest pg-clickhouse-c and clickhouse-c and fix a few issues.

src/binary/insert.c:38:78: error: too few arguments to function call,
      expected 4, have 3
   38 |             pgch_raise(&err, ERRCODE_FDW_ERROR, "could not prepare insert - ");
      |             ~~~~~~~~~~                                                       ^
vendor/pg-clickhouse-c/pg-clickhouse.h:54:1: note: 'pgch_raise' declared
      here
   54 | pgch_raise(const chc_err* err, int sqlstate, const char* what, const char* where);
      | ^          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/binary/insert.c:120:78: error: too few arguments to function call,
      expected 4, have 3
  120 |             pgch_raise(&err, ERRCODE_FDW_ERROR, "could not prepare insert - ");
      |             ~~~~~~~~~~                                                       ^
vendor/pg-clickhouse-c/pg-clickhouse.h:54:1: note: 'pgch_raise' declared
      here
   54 | pgch_raise(const chc_err* err, int sqlstate, const char* what, const char* where);
      | ^          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/binary/insert.c:185:74: error: too few arguments to function call,
      expected 4, have 3
  185 |         pgch_raise(&err, ERRCODE_FDW_ERROR, "could not insert columns - ");
      |         ~~~~~~~~~~                                                       ^
vendor/pg-clickhouse-c/pg-clickhouse.h:54:1: note: 'pgch_raise' declared
      here
   54 | pgch_raise(const chc_err* err, int sqlstate, const char* what, const char* where);
      | ^          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3 errors generated.
make: *** [src/binary/insert.o] Error 1
make: *** Waiting for unfinished jobs....
src/binary/connection.c:319:84: error: too few arguments to function call,
      expected 6, have 5
  319 |         int rc = chc_client_init(&conn->client, &opts, &pgch_alloc, &conn->io, &err);
      |                  ~~~~~~~~~~~~~~~                                                   ^
vendor/pg-clickhouse-c/clickhouse-c/clickhouse-client.h:71:6: note: 
      'chc_client_init' declared here
   71 | int  chc_client_init(chc_client **out, const chc_client_opts *opts,
      |      ^               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   72 |                      const chc_alloc *al, chc_io *io, chc_exception **exc,
      |                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   73 |                      chc_err *err);
      |                      ~~~~~~~~~~~~
src/binary/connection.c:324:13: error: too few arguments to function call,
      expected 4, have 3
  322 |             pgch_raise(
      |             ~~~~~~~~~~
  323 |                 &err, ERRCODE_FDW_UNABLE_TO_ESTABLISH_CONNECTION, "connection error: "
  324 |             );
      |             ^
vendor/pg-clickhouse-c/pg-clickhouse.h:54:1: note: 'pgch_raise' declared
      here
   54 | pgch_raise(const chc_err* err, int sqlstate, const char* what, const char* where);
      | ^          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 errors generated.
make: *** [src/binary/connection.o] Error 1

[theory]

git submodule update --init --recursive