roller-rpc: add %hash-raw-transaction rpc

the returned hash can be used to cancel pending txs
by signing the message 'cancel: 0xke.ccak'

pkg/arvo/app/roller-rpc.hoon

@@ -173,7 +173,8 @@
       %prepare-for-signing     `(hash-transaction id +.params chain:scry | &)
       %get-unsigned-tx         `(hash-transaction id +.params chain:scry & |)
       %get-predicted-state     `(get-naive id +.params predicted:scry)
-      :: TODO: deprecated, remove]
+      %hash-raw-transaction    `(hash-raw-transaction id +.params)
+      :: TODO: deprecated, remove
       ::
       %hash-transaction        `(hash-transaction id +.params chain:scry & |)
     ==

pkg/arvo/app/roller.hoon

@@ -908,7 +908,7 @@
     ::
       =;  hash=@t
         (met 3 hash)^hash
-      (crip "0x{((x-co:co 20) keccak)}")
+      (crip "0x{((x-co:co 65) keccak)}")
     ::
       ~
     ==

pkg/arvo/lib/azimuth-roll-rpc.hoon

@@ -623,6 +623,25 @@
     unsigned-tx:lib
   prepare-for-sig:lib
 ::
+++  hash-raw-transaction
+  |=  [id=@t params=(map @t json)]
+  ^-  response:rpc
+  ?.  =((lent ~(tap by params)) 4)
+    ~(params error:json-rpc id)
+  =+  ^-  $:  sig=(unit @)
+              l2-tx=(unit l2-tx)
+              from=(unit [=ship proxy:naive])
+          ==
+    =,  from-json
+    [(sig params) (tx params) (from params)]
+  ?:  |(?=(~ sig) ?=(~ from) ?=(~ l2-tx))
+    ~(parse error:json-rpc id)
+  =/  tx=(unit tx:naive)  (build-l2-tx u.l2-tx u.from params)
+  ?~  tx  ~(parse error:json-rpc id)
+  :+  %result  id
+  %+  hex:to-json  32
+  (hash-raw-tx:lib u.sig (gen-tx-octs:lib u.tx) u.tx)
+::
 ++  get-naive
   |=  [id=@t params=(map @t json) =^state:naive]
   ^-  response:rpc