improve note in nix_value_force documentation again

[prednaz]

Motivation

the documentation of nix_value_force contains a note that needs fixing.

You don't need this function for basic API usage very often, since all functions that return a Value call [nix_value_force] for you.

this sounds like "all functions that return a Value call [nix_value_force] for you" on the Value that they return. but this is wrong because nix_init_apply, for example, does not call nix_value_force on its return value. indeed, it would be silly because no function could ever return a thunk.

i believe the documentation is trying to say here that "all functions that return a Value call [nix_value_force] for you" on their arguments.

some Value returning functions do not even need to force their arguments because they return a thunk themselves anyway though. so i think the easiest and most accurate statement is as follows.

You don't need this function for basic API usage as long as you use functions that return a Value.

This work is sponsored by Antithesis ✨

Context

i just edited the rest of this note in #10828 but overlooked the misleadingness i am trying to fix here now.

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[prednaz]

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