fix(metadata): map PostgreSQL money to decimal

[hutiefang76]

Purpose

Fixes #4557.

PostgreSQL money columns were falling through the metadata type converter and being reported as STRING. This maps money together with the other PostgreSQL numeric types so it is exposed as Dinky DECIMAL metadata.

Changes

• Treat PostgreSQL money as a decimal-compatible type in PostgreSqlTypeConvert.
• Avoid dereferencing a null precision while checking the existing PostgreSQL decimal precision guard.
• Add a regression test for money metadata conversion.

Verification

JAVA_HOME=$(/usr/libexec/java_home -v 17) PATH="$JAVA_HOME/bin:$PATH" \
  ./mvnw -pl dinky-metadata/dinky-metadata-postgresql -am \
  -Dtest=PostgreSqlDriverTest#convertMoneyTypeToDecimal \
  -DfailIfNoTests=false test

JAVA_HOME=$(/usr/libexec/java_home -v 17) PATH="$JAVA_HOME/bin:$PATH" \
  ./mvnw -pl dinky-metadata/dinky-metadata-postgresql -am \
  -Dtest=PostgreSqlDriverTest \
  -DfailIfNoTests=false test

JAVA_HOME=$(/usr/libexec/java_home -v 17) PATH="$JAVA_HOME/bin:$PATH" \
  ./mvnw -pl dinky-metadata/dinky-metadata-postgresql -am test

All three commands passed locally.