Merge #14582: wallet: always do avoid partial spends if fees are within a specified range

7f13dfb587dd6a7a5b7dfbfe689ae0ce818fe5c9 test: test the implicit avoid partial spends functionality (Karl-Johan Alm)
b82067bf696c53f22536f9ca2e51949c164f6b06 wallet: try -avoidpartialspends mode and use its result if fees are below threshold (Karl-Johan Alm)

Pull request description:

  The `-avoidpartialspends` feature is normally disabled, as it may affect the optimal fee for payments. This PR introduces a new parameter `-maxapsfee` (max avoid partial spends fee) which acts on the following values:
  * -1: disable partial spend avoidance completely (do not even try it)
  * 0: only do partial spend avoidance if fees are the same or better as the regular coin selection
  * 1..∞: use APS variant if the absolute fee difference is less than or equal to the max APS fee

  For values other than -1, the code will now try partial spend avoidance once, and if that gives a value within the accepted range, it will use that.

  Example: -maxapsfee=0.00001000 means the wallet will do regular coin select, APS coin select, and then pick AKS iff the absolute fee difference is <= 1000 satoshi.

  Edit: updated this to reflect the fact we are now using a max fee.

ACKs for top commit:
  fjahr:
    tested ACK 7f13dfb587dd6a7a5b7dfbfe689ae0ce818fe5c9
  achow101:
    ACK 7f13dfb587dd6a7a5b7dfbfe689ae0ce818fe5c9
  jonatack:
    ACK 7f13dfb58, code review, debug build, verified the test fails with `AssertionError: not(2 == 1)` for the number of vouts when `-maxapsfee=0.0001` is changed to 0, and verified the new logging with an added assertion.
  meshcollider:
    Code review ACK 7f13dfb587dd6a7a5b7dfbfe689ae0ce818fe5c9

Tree-SHA512: 475929df57f6191bb4e36bfbcad5a280a64bb0ecd8767b76cb2e44e2301235d0eb294a3f2fac5bbf15d35d7ecfba47acb2285feadb883c9ce31c08377e3afb3c

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