Savings spend flow redesign

[catch-21]

This issue has been converted from a bug that I raised before understanding all the intentions of this savings spend flow.

Behaviour of certain values in the on-chain savings spend flow are unclear and can be confusing, as I've outlined in the comment below.

It would be good to discuss how to improve the UX in this area so it is suitable for basic and advanced use.

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OLD Bug issue:

Describe the bug

When using manual coin selection, it is possible to change the available savings amount by deselecting an input. I'm not sure that this extra validation is useful, but is annoying that I need to go forwards to re-select inputs and go back again to increase the amount being spent. Perhaps only the chosen fee should impact the available savings.

In addition to the above, it seems that the total required is also impacted in an unexpected way on the coin selection screen. See attached screengrab for details.

Reproduce

1. With manual coin selection enabled and two or more utxos
2. Input/Scan an onchain address
3. Input a comfortable amount to send
4. Deselect an input and continue to the review page
5. Go back the amount input page
6. Observe reduced available savings

Screenshots / Recording

NOTE: Notice that not only is the available savings affected by manual coin selection (at 20 seconds) but also the total required goes from 51180 to 31180 on the coin selection page (at 52 seconds).

https://github.com/synonymdev/bitkit/assets/74595920/5ccfa3d0-c531-4a5a-a4c3-fb7836194050

Operating system

Android 13 TKQ1.220829.002

Bitkit version

v117 ae82edd7a3ab8ff771cbf945729e41c43c5ed1f2

Log output

No response