fix: the swap decoder reads each command's type with its router's mask (closes #535)

Each Universal Router address now carries the mask its own source reads a
command's type with: 0x1f for UniversalRouterV1, 0x3f for V1_2 and V2, 0x7f
for V2_1_1 and V2_1_2. The fixed 0x1f dropped the 0x20 bit, so
EXECUTE_SUB_PLAN (0x21) was listed as a V3 exact-out swap. A sub-plan step is
now listed as "Execute Sub-Plan (its steps are not shown)", and a Token In or
Token Out line that nothing named reads "Unknown (could not be decoded)",
since the sub-plan may name it.

Model: opus-5-5

README.md

@@ -1195,9 +1195,10 @@ read:
 The swap's `Token In` and `Token Out` lines name a currency, not an amount; each
 reads `Unknown (not named in the calldata)` when the decoder found no token for
 that side, or `Unknown (could not be decoded)` instead when a V4 swap action in
-the transaction could not be read (see Transaction Decoding below). A V4 step
-with a swap action always sets the output side, and sets the input side only
-when no earlier step set it. It finds each side by three rules:
+the transaction could not be read or the transaction has an `EXECUTE_SUB_PLAN`
+step (see Transaction Decoding below). A V4 step with a swap action always sets
+the output side, and sets the input side only when no earlier step set it. It
+finds each side by three rules:
 
 1. Its input side is the currency its `SETTLE` or `SETTLE_ALL` names, or else
    the one currency that some swap action in the step spends and none buys. Its
@@ -2888,7 +2889,15 @@ Currently supported:
   in the parameter shape deployed on mainnet and Sepolia, not in the newer one
   on `v4-periphery` `main`, which adds a `minHopPriceX36` field. An action in
   any other shape is not read, and its step is listed as
-  `V4 Swap (could not be decoded)`.
+  `V4 Swap (could not be decoded)`. Each step is named by its command type,
+  which the decoder reads from the command byte with the mask the router at that
+  address uses: `0x1f` for `UniversalRouterV1`, `0x3f` for
+  `UniversalRouterV1_2_V2Support` and `UniversalRouterV2`, and `0x7f` for
+  `UniversalRouterV2_1_1` and `UniversalRouterV2_1_2`. The allow-revert flag
+  (`0x80`) therefore does not change a step's name. The decoder does not read
+  the commands inside an `EXECUTE_SUB_PLAN` (`0x21`) step: that step is listed
+  as `Execute Sub-Plan (its steps are not shown)`, and what those commands spend
+  or receive is missing from the other lines.
 
 ### Non-Goals Forever