…thms without restarting wallet

6ed4626 [RPC][Mining] Provide ability to change mining algorithm (Cave Spectre)

Pull request description:

  ### Note
  This is built on top of #876 and also contains a couple corrections to get the `getnetworkhashps` help.

  ### Problem
  In order to switch mining algorithms, you must shut down the wallet and restart with a new `-mine=` flag.

  ### Root Cause
  Never implemented

  ### Solution
  Add `setminingalgo` cli command to allow you to switch between different algorithms.  This RPC command requires you to turn off mining before issuing the command and will error if it does not work.

  ### Testing
  ```
  $ veil-cli help setminingalgo
  setminingalgo algorithm

  Changes your mining algorithm to [algorithm].  Note that mining must be turned off when command is used.

  Arguments:
  1. algorithm   (string, required) Algorithm to mine [progpow, randomx, sha256d].

  Result:
  {
    "success": true|false, (boolean) Status of the switch
    "message": "text",     (text) Informational message about the switch
  }

  Examples:
  > veil-cli setminingalgo sha256d
  > curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "setminingalgo", "params": [sha256d] }' -H 'content-type: text/plain;' http://127.0.0.1:58812/
  ```
  ```
  $ veil-cli setminingalgo randomx
  {
    "success": true,
    "message": "Mining algorithm changed from sha256d to randomx"
  }
   veil-cli getmininginfo
  {
  [...]
    "algorithm": "randomx",
    "difficulty": 0.003707938785486674,
    "networkhashps": 22.73835278085342,
  [...]
  }
  ```
  ```
  $ veil-cli setminingalgo sha257d
  error code: -8
  error message:
  sha257d is not a supported mining type
  $ veil-cli setminingalgo sha256d
  {
    "success": true,
    "message": "Mining algorithm changed from randomx to sha256d"
  }
  $ veil-cli getmininginfo
  {
  [...]
    "algorithm": "sha256d",
    "difficulty": 18.1774015474177,
    "networkhashps": 23.05669884097939,
  [...]
  }
  ```
  ```
  $ veil-cli generatecontinuous true 1
  $ veil-cli setminingalgo progpow
  error code: -8
  error message:
  mining must be stopped to change algorithm
  $ veil-cli generatecontinuous false
  $ veil-cli setminingalgo progpow
  {
    "success": true,
    "message": "Mining algorithm changed from sha256d to progpow"
  }
  $ veil-cli getmininginfo
  {
  [...]
    "algorithm": "progpow",
    "difficulty": 164.7481194885794,
    "networkhashps": 23.16038554216868,
  [...]
  }
  ```

Tree-SHA512: 89c8a5032856afcf48ba0ec6c0c9636d9f451e705efe1b9545c3b1719e7db7897d6721a5bf2663f4e3b0d05600c46acff5b6e9c4dd7d3ec3ab2fc47311a328d4