Require peft>=0.17.0 and drop the target_parameters guards - #7640

This PR raises the peft floor from 0.13.0 (September 2024) to 0.17.0 (August 2025) and removes the guards that floor made necessary.

Part of #7644.

Motivation

peft 0.13.0 is 24 months old, so under the criterion in #7116 it can be dropped without further justification. 0.17.0 is the newest release the same criterion allows today, since it is 14 months old and the rule does not require anything younger than 1 year.

LoraConfig.target_parameters was introduced in peft 0.17.0, so everything #7119 added to keep 0.13 through 0.16 working becomes dead at this floor.

Changes

• Raise peft>=0.13.0 to >=0.17.0 in the peft extra and in dev
• Drop the Version("0.17.0") <= lower bound from the reference-adapter guard in the DPO, GRPO, KTO and RLOO trainers, and the comment sentence explaining it
• Pass target_parameters to LoraConfig directly in get_peft_config again, instead of only when set
• Remove the require_peft_target_parameters test mark and restore @require_peft on the six tests that used it

The < Version("0.20.0") upper bound stays: it encodes peft#3340, fixed by peft#3350 in 0.20.0, and 0.17 to 0.19 are still supported.