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)". Its commands are
not read and may spend from or pay the user wherever the step stands, so with
one the summary names no swap direction, Token In and Token Out read
"Unknown (could not be decoded)", and there is no Amount or Min. received.

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, which leaves both sides unknown (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
@@ -2892,7 +2893,18 @@ 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, and wherever that
+  step stands they may spend the user's tokens or pay the user. That step is
+  listed as `Execute Sub-Plan (its steps are not shown)`, and whatever the other
+  steps state, the summary names no swap direction, `Token In` and `Token Out`
+  read `Unknown (could not be decoded)`, and there is no `Amount` or
+  `Min. received` line.
 
 ### Non-Goals Forever