feat: Phase 8.2, 8.4, 8.5, 9.1 + C backend fixes

Phase 8.2 — Gradual Ownership:
- Add tkRef/tkMutRef types and `mut` keyword
- Add @[Checked] attribute for opt-in borrow checking
- Reject assignment through &T in checked functions
- examples/ownership.bux

Phase 8.4 — CTFE:
- Evaluate const func at compile-time via evalExpr/evalBlock
- Fold const declarations to literals; emit #define in C
- examples/ctfe.bux (Factorial(10) → 3628800)

Phase 8.5 — Trait Bounds:
- Change declFuncTypeParams from seq[string] to seq[TypeParam] (name + bound)
- Parser handles <T: Comparable>
- Sema checks typeImplements at call sites
- Fix C backend: generic receivers + pointer self field access
- examples/trait_bounds.bux

Phase 9.1 — Package Manager:
- Inline tables/arrays in TOML parser
- bux add, bux install, bux.lock generation
- Dependency resolution with git/path sources
- Build pipeline merges dependency .bux sources

C Backend Fixes:
- resolveExprType(ekIdent) now applies typeSubst for generic params
- Method desugaring works for monomorphized generic receivers
- Pointer checks use isPointer (covers tkRef/tkMutRef)
- Field access on &T emits -> instead of .

Remove accidentally committed test binaries from tracking

src/token.nim

@@ -50,6 +50,7 @@ type
     tkSuper           # super
     tkSizeOf          # sizeof
     tkOwn             # own (gradual ownership transfer)
+    tkMut             # mut (mutable reference)
     tkDiscard         # discard (evaluate and throw away)
 
     ##Punctuation
@@ -142,7 +143,7 @@ proc isKeyword*(kind: TokenKind): bool =
      tkBreak, tkContinue, tkReturn, tkMatch,
      tkFunc, tkLet, tkVar, tkConst, tkType, tkStruct, tkEnum,
      tkUnion, tkInterface, tkExtend, tkModule, tkImport,
-      tkPub, tkExtern, tkAs, tkIs, tkNull, tkSelf, tkSuper, tkOwn, tkDiscard:
+      tkPub, tkExtern, tkAs, tkIs, tkNull, tkSelf, tkSuper, tkOwn, tkMut, tkDiscard:
     true
   else:
     false
@@ -197,6 +198,7 @@ proc keywordKind*(text: string): TokenKind =
   of "super": tkSuper
   of "sizeof": tkSizeOf
   of "own": tkOwn
+  of "mut": tkMut
   of "discard": tkDiscard
   of "true", "false": tkBoolLiteral
   else: tkIdent
@@ -242,6 +244,7 @@ proc tokenKindName*(kind: TokenKind): string =
   of tkSelf: "'self'"
   of tkSuper: "'super'"
   of tkOwn: "'own'"
+  of tkMut: "'mut'"
   of tkDiscard: "'discard'"
   of tkLParen: "'('"
   of tkRParen: "')'"