test: record PostgreSQL expression coverage gains and API contracts

Refresh the pinned PostgreSQL 18.4 accepted-statement inventory, selected CI
fixtures and compatibility report after the native expression grammar changes.
The 51,415-statement corpus now contains 26,243 complete-input AST results,
up 7,104 from 19,139 before this expression phase. All transitions are gains:
7,074 trailing-input and 30 partial cases become complete; no previously
complete case is lost. Newly complete statements comprise 6,454 SELECT,
310 INSERT, 268 EXPLAIN, 55 UPDATE, 14 DELETE, two SET and one CALL.

Document canonical cast emission, typed-literal length preservation, lexical
type leaves, PostgreSQL symbolic operator precedence, collation and named
arguments. Explain bind preservation, appended token/node kinds, planner
rejection and remaining grammar limits. Update the AST parameterization guide
because supported PostgreSQL CAST and typed string constants now rewrite
correctly instead of being rejected as generic functions or string aliases.
Retain the authorized phase plan, review rulings and completion evidence.

The source commit recorded in the report identifies the same parser sources
as the working tree measured immediately before committing. Complete-input
coverage checks status, classification, AST presence and consumption; it is
not semantic equivalence or a representative production-workload percentage.
Type/operator/catalog resolution and complete PostgreSQL grammar remain
outside the scope of this increment.

Validation: 1,370 C++ tests pass with 37 backend-dependent skips; all 42 focused
AST/expression tests pass under ASan/UBSan; all 87 compatibility harness tests
and 26,835 refreshed CI fixtures pass. Forty-six focused SQL reconstructions
match PostgreSQL ASTs after source positions are removed, and independent
review checks all 494 keyword classifications plus ten argument cases.
Benchmarks, reports of timings and benchmark build artifacts remain local.

Author: renecannao

docs/ast-utilities.md

@@ -111,15 +111,20 @@ CURRENT_TIME, LOCALTIME, and LOCALTIMESTAMP remains a syntax constant. MySQL als
 preserves precision arguments of NOW, CURTIME, SYSDATE, UTC_TIME, and
 UTC_TIMESTAMP; these ordinary function names retain bindable arguments in
 PostgreSQL. Quoted function names retain bindable arguments in both dialects.
-Aggregate FILTER predicates and window frame offsets are bindable. A manually constructed binary `::` AST is supported; this does not
-extend the parser's existing cast grammar.
+Aggregate FILTER predicates and window frame offsets are bindable. PostgreSQL
+casts and type-prefixed string literals now produce `NODE_TYPE_CAST` with an
+expression child and a `NODE_TYPE_NAME` leaf. Cast values are bindable; type
+modifiers and array bounds remain intact. Named function argument values are
+bindable while their names remain intact. Manually constructed binary `::`
+ASTs retain their existing support.
 
 Unsupported roots and contexts return `UnsupportedRoot` or `UnsupportedContext`
 with no AST or partial mapping. These include SET/transaction/COPY/DDL/other
 utility statements, SELECT INTO, CTEs, generic function-shaped CAST nodes,
 opaque subquery/interval fragments, and unknown future node types. PostgreSQL
-string-shaped aliases are rejected, including typed string literals currently
-misparsed as aliases (for example, `SELECT TIMESTAMP '2020-01-01'`). These
+string-shaped aliases are rejected. Supported type-prefixed literals such as
+`SELECT TIMESTAMP '2020-01-01'` now parameterize as casts instead of being
+misparsed as aliases. These
 restrictions reflect contexts where replacing literals or the current emitter
 would not produce reliable executable SQL. Parameterization does not change the
 existing digest API.