feat: NCS-31 FastParse FEN (#22)

Summary

  - Added fastparse_3:3.0.2 dependency to modules/io
  - Implemented FenParserFastParse as a second alternative FEN parser using FastParse, with the same public API as
  FenParser and FenParserCombinators
  - Parsers are built bottom-up using (using P[Any]) Scala 3 syntax with NoWhitespace.* to prevent implicit whitespace
  skipping; rank sum validation uses Pass/Fail inside .flatMap
  - Added FenParserFastParseTest mirroring FenParserCombinatorsTest to prove behavioural equivalence across all three
  implementations

  Test plan

  - All existing tests pass — FenParser, FenParserCombinators, and all other modules untouched
  - FenParserFastParseTest covers all cases: valid FEN, invalid color, invalid castling, invalid board shapes, en
  passant, rank overflow, round-trip via FenExporter
  - All parser logic branches genuinely covered — known scoverage gap documented in docs/unresolved.md (FastParse inline
   macro generates synthetic proxy methods that scoverage instruments but that never execute at runtime)

Co-authored-by: LQ63 <lkhermann@web.de>
Reviewed-on: #22
Reviewed-by: Janis <janis-e@gmx.de>
Co-authored-by: Leon Hermann <lq@blackhole.local>
Co-committed-by: Leon Hermann <lq@blackhole.local>

build.gradle.kts

@@ -33,7 +33,8 @@ val versions = mapOf(
     "SCALAFX"               to "21.0.0-R32",
     "JAVAFX"                to "21.0.1",
     "JUNIT_BOM"             to "5.13.4",
-    "SCALA_PARSER_COMBINATORS" to "2.4.0"
+    "SCALA_PARSER_COMBINATORS" to "2.4.0",
+    "FASTPARSE" to "3.0.2"
 )
 extra["VERSIONS"] = versions