Add more accessors to mammoth classes

lib/mammoth/include/mammoth/channel.h

@@ -8,6 +8,7 @@ class Channel {
   Channel() {}
   void adopt_cap(uint64_t id);
   uint64_t release_cap();
+  uint64_t cap();
 
   z_err_t WriteStr(const char* msg);
   z_err_t ReadStr(char* buffer, uint64_t* size);

lib/mammoth/include/mammoth/memory_region.h

@@ -15,6 +15,9 @@ class MappedMemoryRegion {
 
   uint64_t paddr() { return paddr_; }
   uint64_t vaddr() { return vaddr_; }
+  uint64_t size() { return size_; }
+
+  uint64_t cap() { return vmmo_cap_; }
 
   operator bool() { return vmmo_cap_ != 0; }