perf(signals): avoid unecessary observable conversions in rxMethod

[markostanimirovic]

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)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

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

What is the current behavior?

rxMethod converts signals and static inputs into observables.

What is the new behavior?

rxMethod does not convert signals and static inputs into observables which reduces more than 1kB.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

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