Minimal RFC 6570 Level-1 URI Template matcher and expander.

Used by the server's resources/read handler to route a concrete URI to a registered resource_template. We only implement Level 1 ({var} simple expansion) — that covers every template the spec's reference examples use, and it's the level the MCP server registry actually accepts.

Examples:

   match(<<"file:///etc/hosts">>, <<"file:///{path}">>).
     %% => {ok, #{<<"path">> => <<"etc/hosts">>}}
  
   match(<<"https://api.x/v1/users/42">>,
         <<"https://api.x/v1/{kind}/{id}">>).
     %% => {ok, #{<<"kind">> => <<"users">>,
     %%          <<"id">>   => <<"42">>}}
  
   expand(<<"file:///{path}">>, #{<<"path">> => <<"etc/hosts">>}).
     %% => {ok, <<"file:///etc/hosts">>}