fix: switch lowering supports any number of cases (was capped at 8)

Replaced fixed-size locals (c0..c7) with O(n^2) linked-list walk
that handles arbitrary case counts via reverse-index traversal.
Added switch.bux test with 11 and 10 cases.

Makefile

@@ -5,7 +5,7 @@ BUILD_DIR := build
 # Project-local nimcache so CI can cache compiles (default is ~/.cache/nim).
 NIMFLAGS ?= --nimcache:nimcache
 
-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 ownership_checked ownership_release drop_early_return lifetime_elision ctfe ctfe_crc async concurrency os_time process json iter trait_bounds channel sync jwt stdlib_ergonomics tuples func_ptr map_remove array_iter_extra string_extra multi_closure iter_hof closure_control match_let string_interp iter_generic generic_infer_hof struct_tuple_pat match_block nested_patterns match_guards pattern_shadow move_field move_field_partial move_field_remaining move_field_nested move_field_ptr move_cross_fn c_precedence macro_twice macro_repeat macro_nested macro_hygiene macro_unhygienic macro_stmt_pat macro_tt macro_tt_raw macro_type collections_extra generic_enum
+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 ownership_checked ownership_release drop_early_return lifetime_elision ctfe ctfe_crc async concurrency os_time process json iter trait_bounds channel sync jwt stdlib_ergonomics tuples func_ptr map_remove array_iter_extra string_extra multi_closure iter_hof closure_control match_let string_interp iter_generic generic_infer_hof struct_tuple_pat match_block nested_patterns match_guards pattern_shadow move_field move_field_partial move_field_remaining move_field_nested move_field_ptr move_cross_fn c_precedence macro_twice macro_repeat macro_nested macro_hygiene macro_unhygienic macro_stmt_pat macro_tt macro_tt_raw macro_type collections_extra generic_enum switch
 
 # Platform smoke (macOS CI): full EXAMPLES still runs on Linux.
 EXAMPLES_SMOKE := hello ownership ownership_release strings map move_field move_field_partial move_field_remaining move_field_nested move_field_ptr move_cross_fn c_precedence macro_twice macro_repeat macro_nested macro_hygiene macro_unhygienic macro_stmt_pat macro_tt macro_tt_raw ctfe_crc