misc: bump p3 version to =0.4.3 (#28)

* Update to p3 0.4.1 and fix clippy regressions

* Use p3::field re-exports

* Use p3 field reexports in curves

* Drop redundant p3-field dependency

* Remove unused PrimeCharacteristicRing imports

* Bump p3 to 0.4.3 and remove test binary

* chore: remove redundant field bounds

* chore: simplify implied trait bounds

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Co-authored-by: kunxian xia <xiakunxian130@gmail.com>

Author: hero78119

.github/PULL_REQUEST_TEMPLATE.md

@@ -24,4 +24,3 @@ When Copilot reviews this PR, apply `.github/copilot-instructions.md` strictly.
 - Prioritize soundness, performance, and architecture risks over style.
 - Output order: findings by severity, then open questions, then brief summary.
 - If PR description is empty or missing key context, report `PR metadata: description` as a finding.
-