feat: NCS-30 FEN Parser using ParserCombinators (#21)

Summary

  - Added scala-parser-combinators_3:2.4.0 dependency to modules/io
  - Implemented FenParserCombinators as an alternative FEN parser using RegexParsers, with the same public API as the
  existing FenParser
  - Parsers are built bottom-up: piece characters → rank tokens → rank → board, composed with explicit field separators
  into a full FEN parser
  - Added FenParserCombinatorsTest mirroring the existing FenParserTest to prove behavioural equivalence

  Test plan

  - All existing tests pass — FenParser and all other modules untouched
  - FenParserCombinatorsTest covers all cases: valid FEN, invalid color, invalid castling, invalid board shapes, en
  passant, round-trip via FenExporter
  - 100% line/branch/method coverage on FenParserCombinators

Co-authored-by: LQ63 <lkhermann@web.de>
Reviewed-on: #21
Reviewed-by: Janis <janis-e@gmx.de>
Co-authored-by: Leon Hermann <lq@blackhole.local>
Co-committed-by: Leon Hermann <lq@blackhole.local>

modules/io/build.gradle.kts

@@ -38,6 +38,8 @@ dependencies {
         }
     }
 
+    implementation("org.scala-lang.modules:scala-parser-combinators_3:${versions["SCALA_PARSER_COMBINATORS"]!!}")
+
     implementation(project(":modules:api"))
     implementation(project(":modules:rule"))