migrate to new mutable decl syntax

source/strpool/strpool.hon

@@ -3,7 +3,7 @@ import "@std/arraylist"
 import "@std/hashmap"
 
 # cross-cutting concern, hence global singleton (owned by main.hon)
-strings StringPool = undefined
+strings StringPool := undefined
 
 InternError :: enum { out_of_space }
 

source/strpool/strpool.test.hon

@@ -2,10 +2,10 @@ import "@std/mem"
 import "@std/testing"
 
 handles_intern test {
-    pool StringPool = init(mem.c_allocator)
+    pool StringPool := init(mem.c_allocator)
     defer deinit(&pool)
 
-    input [5]mut u8 = ['h', 'e', 'l', 'l', 'o']
+    input [5]mut u8 := ['h', 'e', 'l', 'l', 'o']
     id :: try intern(&pool, input[..])
     duplicate :: try intern(&pool, "hello")
     input[0] = 'j'