parse: move test binaries into a single directory

CMakeLists.txt

@@ -606,7 +606,8 @@ if (TESTS)
         matrix
         memory/deleter
         parallel/queue
-        parse
+        parse/value
+        parse/si
         point
         polynomial
         pool
@@ -618,7 +619,6 @@ if (TESTS)
         rational
         region
         roots/bisection
-        si
         signal
         singleton
         stream

parse/si.hpp

@@ -14,6 +14,7 @@
 #include <system_error>
 
 namespace cruft::parse {
+    /// Parse a number with an SI suffix. eg, 10K for 10 * 1024
     template <typename ValueT>
     expected<ValueT, std::errc>
     si (cruft::view<char const*>);