Scala parser: eliminate J.Unknown, add S types for Scala-specific constructs

[jkschneider]

Summary

• visitUnknown now throws UnsupportedOperationException instead of producing J.Unknown — gaps surface immediately as test failures
• Added S.StatementExpression (replaces S.BlockExpression) — wraps any J to make it both Statement and Expression, following K.StatementExpression pattern
• Added S.TypeAscription — proper S type for expr: Type (not J.TypeCast)
• Added S.TypeAlias — type alias declarations (type Foo = Bar)
• Added S.PatternDefinition — destructuring declarations, enum cases, given definitions
• Curried parameter lists modeled as compositional J.Lambda chain with Curried marker
• OmitBraces marker on blocks without source braces; printer skips { }
• CLAUDE.md updated: J.Unknown is forbidden, markers must not carry LST elements

New parser handlers

• ParsedTry, This, InterpolatedString, SymbolLit, NamedArg, ByNameTypeTree, TypeBoundsTree, TypeApply (classOf), Alternative catch patterns, Bind (at-binding), match case guards

Fixes

• Template matching: preserve /*__p0__*/ comment in method name prefix for parameter detection
• Space before : in given declarations preserved via varargs field
• Block arguments: extract lambda from J.Return wrapper; OmitBraces on braceless blocks
• Procedure syntax body re-parsing for Scala 3 compiler desugaring
• Match case guard whitespace preservation
• Multi-statement case body printing

Test plan

• 433 tests, 0 failures, 0 skipped