common : inhibit lazy grammar sampler while reasoning is active (#20970)

* common : inhibit grammar while reasoning budget is active

* cont : update force_pos in accept

* cont : fix tests

* cont : tweak should apply logic

* cont : return early not using grammar sampler

* Add tests

* cont : prevent backend sampling when reasoning budget enabled

* cont : fix typo

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Co-authored-by: Piotr Wilkin <[email protected]>