fix(hir_lower): generic monomorphization for cross-module generic calls

The old findGenericCalls second-pass only looked in non-generic functions
and generated unresolved instances like Array_Get_T when generic funcs
called other generic funcs. Removed it entirely.

lowerExpr for ekCall now invokes generateMethodInstance directly for
both explicit (ekGenericCall) and inferred generic calls. This ensures
concrete instantiations are generated on-demand with correct typeSubst.

Also added guard in resolveTypeExpr/substituteType to skip emitting C
struct definitions for unresolved type parameters (e.g. Array<T> inside
a generic function body before monomorphization).

feat(std): add Std::Iter module
- Array_Iter, Iter_Next, Iter_HasNext, Iter_Peek, Iter_Reset
- Iter_Pos, Iter_Len, Iter_Count, Iter_Skip, Iter_Take

docs: document Std::Iter in Stdlib.md
examples: add iter.bux example
tests: add _test_array regression test

Makefile

@@ -3,7 +3,7 @@ SRC := compiler/bootstrap/main.nim
 OUT := buxc
 BUILD_DIR := build
 
-EXAMPLES := hello fibonacci factorial structs enums methods algebraic_enums generics generics_struct generic_infer generic_infer2 extend_generic pattern_matching strings strings2 map result_option try_operator ownership ctfe async concurrency os_time process json
+EXAMPLES := hello fibonacci factorial structs enums methods algebraic_enums generics generics_struct generic_infer generic_infer2 extend_generic pattern_matching strings strings2 map result_option try_operator ownership ctfe async concurrency os_time process json iter
 
 .PHONY: all build dev test clean test-examples