Fix MultiSwapper quote backcompat

[liobrasil]

Summary

This follow-up fixes two behavioral regressions introduced by the current MultiSwapper quote changes, while keeping the improved route-selection logic already in the branch.

Problem

The current branch correctly preserves the chosen inner route's real quote values so MultiSwapper can pick the right route.

That change also altered the public quote shape returned by MultiSwapper, and two existing callers rely on the previous behavior:

1. swap(nil, ...) can fail with strict or capacity-limited inner swappers.
   quoteOut(forProvided) may now return a smaller inAmount than the vault balance forwarded by _swap, which creates a mismatch for connectors that enforce inVault.balance <= quote.inAmount.
   Example: quoteOut(100) picks a capped route and returns inAmount = 60, but _swap still forwards a vault with balance 100.

2. SwapSource.withdrawAvailable(maxAmount) can return more than maxAmount.
   quoteIn(forDesired) may now return an outAmount larger than the requested amount, and SwapSource returns that swap result directly.
   Example: withdrawAvailable(10) uses quoteIn(10), but the quote returns outAmount = 10.00000002, so the caller gets more than 10.

Fix

Keep the current route-selection logic, but restore the previous outward quote semantics expected by those callers:

• quoteIn(forDesired) caps full-route outAmount to forDesired
• quoteOut(forProvided) keeps inAmount = forProvided

This preserves the selection fix while removing the caller regressions.

Tests

• flow test ./cadence/tests/SwapConnectorsMultiSwapper_test.cdc
• added a regression test for swap(nil, ...) with a strict capped inner swapper
• added a regression test for SwapSource.withdrawAvailable(maxAmount) not exceeding maxAmount