Regression: Switch to cmds lib 1.0 Changes Behaviour of WithDefault

It seams that the new command library changes the behavior of `WithDefault` (previous called just `Default` before #4403). From what I can tell it changes it in two ways:

(1) Using WithDefault interfere with discovering if that option was specified on the command line. For example I noticed these changes in the core/commands/add.go (in commit 4909c5a56d256e0b999d11b065227b94576609ce):
```diff
- cmdkit.IntOption(cidVersionOptionName, "Cid version. Non-zero value will change default of 'raw-leaves' to true. (experimental)").WithDefault(0),
+ cmdkit.IntOption(cidVersionOptionName, "CID version. Defaults to 0 unless an option that depends on CIDv1 is passed. (experimental)"),
```

```diff
- hashFunStr, hfset := req.Options[hashOptionName].(string)
+ hashFunStr, _ := req.Options[hashOptionName].(string)
```

(2) I noticed that when WithDefault is used a value is always passed with the API when before I am fairly sure it was not.

I am not 100% sure but it appears that using WIthDefault sets a value client side rather when doing the intended purpose of this function and setting an alternative default server side.

Related: #4911

CC @keks @Stebalien

Start with core/commands/add.go and compare the WithDefault changes from commit 4909c5a56d256e0b999d11b065227b94576609ce, then read the related discussion in #4911. Reproduce whether WithDefault affects command-line option detection and values sent through the API; the work is done when both behaviors match the intended server-side default semantics.

Written by the indexing model from the issue text.