…oercion in comparisons and predicates

Type coercion previously handled only microsecond TimestampType when one
operand of a comparison or predicate is a string: the string was cast to
TimestampType so subsecond digits compared exactly. Nanosecond timestamp
types (Timestamp{LTZ,NTZ}NanosType) had no such arm, so a string compared
against a nanos column fell through to generic handling and lost the 7th-9th
fractional digits.

This adds the missing non-ANSI arms, mirroring the existing microsecond
handling: two Equality arms in StringPromotionTypeCoercion cast the string to
the concrete nanos operand type, and two findCommonTypeForBinaryComparison
cases in TypeCoercion return that nanos type for the range path. The concrete
family and precision of the timestamp operand are preserved, the arms are
ordered so equality fires before the range path, and legacy
castDatetimeToString is honored (range promotes both sides to string, equality
still casts the string to nanos). ANSI type coercion is intentionally left
unchanged.

Tests: TypeCoercionSuite "binary comparison with string promotion" gains
nanos assertions (all precisions, both families, plus a legacy-mode block that
exercises the new arms); TimestampNanosWideningSuiteBase adds an end-to-end
string-operand test; and the timestamp-{ltz,ntz}-nanos golden files add
equality/range/BETWEEN cases.

Co-authored-by: Isaac

…7811-nanos

# Conflicts:
#	sql/core/src/test/resources/sql-tests/analyzer-results/timestamp-ltz-nanos.sql.out
#	sql/core/src/test/resources/sql-tests/analyzer-results/timestamp-ntz-nanos.sql.out
#	sql/core/src/test/resources/sql-tests/inputs/timestamp-ltz-nanos.sql
#	sql/core/src/test/resources/sql-tests/inputs/timestamp-ntz-nanos.sql
#	sql/core/src/test/resources/sql-tests/results/timestamp-ltz-nanos.sql.out
#	sql/core/src/test/resources/sql-tests/results/timestamp-ntz-nanos.sql.out