migration algorithm exits without processing all inputs.

# Context

The migration algorithm is an iterative algorithm, which attempts to construct several coin selections in order to deplete a wallet. An initial "ideal batch size" is calculated beforehand, and then, the algorithm proceed to construct selections from batch of inputs of that ideal size (modulo the last batch).

Constructing a selection also means _balancing it_. Here, the algorithm will depletes change outputs until reaching an equilibrium and will take care of filtering out dust coins that are below a certain threshold.

There are cases where a given selection could not produce any value (all change output are below the threshold).

# Expected Behavior

The algorithm should discard such "no-value" selections, and continue processing next batches until it has traversed all batches.

# Current Behavior

The algorithm stops at the first "no-value" selections and returns, with whatever selections has been accumulated this far, possibly leaving many inputs behind.

# Resolution

https://github.com/input-output-hk/cardano-coin-selection/blob/cff368d674fe58bc1a12e6564a26ccea21eb5aac/src/library/Cardano/CoinSelection/Algorithm/Migration.hs#L108-L112

The issue is the handling of the `Nothing` branch :point_up: which should not be `pure []` (terminal case of the recursion) but simply `migrate`, discarding the ongoing selection, but continuing migrating others.

The migration loop is in src/library/Cardano/CoinSelection/Algorithm/Migration.hs; start by reading lines 108-112, especially the Nothing branch, and trace how migrate processes batches. Done means a no-value selection is discarded while later batches continue processing, so all inputs are traversed.

Written by the indexing model from the issue text.