Refactor EcOps (and FieldArith) from type-level tag to stateful &mut self trait

[ocdbytes]

Problem

The EcOps trait (and its supertrait FieldArith) currently acts as a type-level tag rather than a proper interface. Every method takes compiler,
range_checks, and params as explicit arguments:

  pub trait EcOps: FieldArith {
      fn point_double(
          compiler: &mut NoirToR1CSCompiler,
          range_checks: &mut BTreeMap<u32, Vec<usize>>,
          params: &MultiLimbParams,
          p: EcPoint,
      ) -> EcPoint;
      // ...
  }

NativeEcOps ignores _range_checks entirely, making the signature dishonest about what each impl actually needs. The same pattern exists in FieldArith
(field_add, field_sub, etc.).

Ref: #310 (comment)

Proposed Solution

Make methods take &mut self so each impl carries its own state:

  pub trait EcOps {
      fn point_double(&mut self, p: EcPoint) -> EcPoint;
      fn point_add(&mut self, p1: EcPoint, p2: EcPoint) -> EcPoint;
      fn verify_on_curve(&mut self, p: EcPoint);
  }

Each impl struct would hold the state it actually needs:

  pub struct NativeEcOps<'a> {
      compiler: &'a mut NoirToR1CSCompiler,
      params: &'a MultiLimbParams,
      // no range_checks — native doesn't need them
  }

  pub struct NonNativeEcOps<'a> {
      compiler: &'a mut NoirToR1CSCompiler,
      range_checks: &'a mut BTreeMap<u32, Vec<usize>>,
      params: &'a MultiLimbParams,
  }

Same refactor applies to the FieldArith supertrait — field_add, field_sub, etc. should also move to &mut self.