feat(signals): set state in patchState to readonly

[rainerhahnekamp]

As discussed in #4030, the update function of patchState, provides the state as deep readonly.

Notes on the test: I've decided to go with @ts-expect-error instead of ts-snippet. ts-snippet requires the source code as string, whereas @ts-expect-error can be applied to normal code. This makes it easier to write but also to refactor.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
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PR Type

What kind of change does this PR introduce?

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

What is the current behavior?

Closes #4030

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

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[jits]

The type-fest library has a more comprehensive version of this: https://github.com/sindresorhus/type-fest/blob/main/source/readonly-deep.d.ts. I can't tell the differences off the top of my head but thought I'd mention it.

(Note: I'm not advocating using the type-fest library as a dependency — more providing this in case of inspiration for some good 'ol copy-pasting :))

[rainerhahnekamp]

Hey @jits, I took a look at it before. It supports a lot of types that are not allowed to be part of the state object. So I took arrays, primitive types and nested objects out of it.

[jits]

Hi @rainerhahnekamp — ahh, perfect! Thanks for clarifying. (And that makes a lot of sense)

[markostanimirovic]

I suggest keeping types as they are and displaying a warning in dev mode if the state is mutated.