Extract DeclaredType parsing from LibsqlResultSetMetaData #204

Goal

Collapse the declared-type parsing in LibsqlResultSetMetaData into one value object. Three regexes and four matcher blocks currently encode the same "declared type or cast fallback" idea, and each getter repeats the null and empty handling.

Depends on

#203. Same file.

Pin

LibsqlResultSetMetaDataTest covers lower-case cast only, whitespace preservation in type names, malformed precision throwing NumberFormatException, and precision and scale from a parenthesized type.

Scope

• Create DeclaredType with of(Col), typeName(), precision(), scale(), and isDeclared() from LibsqlResultSetMetaData 22 to 25, 160 to 184, 290 to 300, and 342 to 358.
• getPrecision, getScale, getColumnTypeName, and isSigned delegate.

Preserve

• getColumnTypeName preserves internal whitespace and upper-cases with Locale.ENGLISH.
• getPrecision parses with Integer.parseInt and throws NumberFormatException unchecked.
• getScale returns 0 unless there are exactly two comma-separated parts.
• The cast fallback matches lowercase cast only and uses the original column name.

Acceptance

• DeclaredType.java exists and holds the moved logic unchanged.
• LibsqlResultSetMetaData.java is under 430 lines.
• ./mvnw -pl libsql-jdbc -am test green with no assertion edited.
• ./mvnw spotless:check green.