feat: Implement Strategy Ranking and Fallback Mechanism for Strategy Execution

Currently, Barq simply selects the best strategy and attempts to execute the payment. If it fails, no other strategies are tried. It should instead try alternative strategies if the payment fails and continue to try until all strategies are exhausted.

When a strategy fails, another strategy has to be tried. Decide on a metric to rank strategies and order them so we can select the best strategy first and try the next best if the first one fails.

Start by tracing the current strategy selection and payment execution flow described in the issue. Define and document a ranking metric, then verify that execution tries strategies in order until one succeeds or all strategies are exhausted; add tests for fallback and complete failure if the repository provides corresponding test locations.

Written by the indexing model from the issue text.