fix: a swap's unknown first take shows beside a PERMIT2_TRANSFER_FROM, only when the user pays it (closes #634)

decode() now records whether the user pays the V4 step that sets the
input side any of its input token, and decides once, after the loop,
whether that step counts as a take from the sender. A stated amount
counts whoever pays it; with none stated, the step counts only when the
user pays it. Paid from the router, it gets no Moved from the sender
lines, with a PERMIT2_PERMIT of another token or without. When it counts
and states no amount, its Unknown (could not be decoded) line also shows
beside a PERMIT2_TRANSFER_FROM of its token, whose figure is on that
move's own lines or, into the router, on its Paid to line. README
Transaction Decoding says the same.

Model: opus-5-5

README.md

@@ -3185,7 +3185,8 @@ Currently supported:
   step whose input it cannot read, in whole or in part, and a step it fails on.
   In any other case the line gives the total, as with no permit. When the step
   that sets the input side spends a token other than the permit's, or one the
-  decoder does not know, its amount gets lines of its own and the total has no
+  decoder does not know, its amount gets lines of its own, unless it states no
+  amount and the user pays it none of its input token, and the total has no
   figure to start from: unless the permit's amount stands there is no `Amount`
   line, and each take of the permit's token gets lines of its own. Each take the
   total does not count gives three lines after the `Amount` line (after
@@ -3193,11 +3194,16 @@ Currently supported:
   `Token In` after an amount that is not a quantity (a V4 open delta,
   `ALREADY_PAID`, which keep their wording on the `Amount` line, or no stated
   amount, as of a V4 exact-out step); and one whose amount the decoder does not
-  know. When the step that sets the input side states no amount and there is no
-  `Amount` line, that step gets them too whenever another take's lines give a
-  figure, so that figure cannot read as all that leaves. They come in step
-  order, the step that sets the input side first when it has them:
-  `Moved from the sender`, its amount, worded as the `Amount` line words one, or
+  know. When the step that sets the input side states no amount, the user pays
+  it some of its input token, and there is no `Amount` line, that step gets them
+  too whenever another take's lines give a figure, or a `PERMIT2_TRANSFER_FROM`
+  of its token gives one, on the lines below or, into the router, on its
+  `Paid to` line, so that figure cannot read as all that leaves. When it states
+  no amount and the user pays it none of its input token, as when the router
+  pays it, that step takes none of that token from the user's wallet and never
+  gets them, with a permit or without. They come in step order, the step that
+  sets the input side first when it has them: `Moved from the sender`, its
+  amount, worded as the `Amount` line words one, or
   `Unknown (could not be decoded)` when the decoder does not know it;
   `Token moved`, giving the token's address as the `Token In` line does; and
   `Moved to`, which reads `The swap step that spends it`. A token the decoder