fix(signals): export DeepSignal

[timdeschryver]

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PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
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[ ] Other... Please describe:

What is the current behavior?

Closes #4372

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

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[matheo]

@timdeschryver is it possible to export toDeepSignal too?
other open source libraries can take advantage of it without duplicating it :(

[rainerhahnekamp]

@matheo, is signalState() not already the toDeepSignal you are looking for?

[matheo]

@rainerhahnekamp thanks for the answer!
the requirement is to convert and keep track of a changing snapshot:
niklas-wortmann/xstate-angular#13
so every time the state-machine is updated, we get a refreshed DeepSignal like here:
https://github.com/niklas-wortmann/xstate-angular/blob/main/lib/xstate-ngx/src/lib/useSelector.ts

it doesn't fit quite well right? we need to support primitive data types and not only objects
as we can select single-values of the context (the only object), or the value/error/output of the state-machine, etc.

[timdeschryver]

@matheo will you be installing the @ngrx/signals package just to have the toDeepSignal method available?

I think it would be better to create a new issue with this request and explain the need why it will be useful to also export toDeepSignal. We try to keep our public API to a minimum to make it easier to change in the future without introducing breaking changes.