Remove local Plonky3 workarounds where upstream now supports them

[adr1anh]

We maintain several extension traits and copied code to work around missing upstream Plonky3 features. Some of these have since been merged upstream and can be replaced.

Ready to remove

• BitReversibleMatrix trait copy (lmcs/bitrev.rs) — Marked "Temporary stopgap." Upstream matrix: implement BitReversibleMatrix for wrapper types Plonky3/Plonky3#1456 adds impls for FlatMatrixView and wrapper types.
• PackedValueExt::pack_columns (lmcs/utils.rs) — Upstream Add broadcast, pack_columns, pack_columns_fn, and unpack_iter to PackedValue Plonky3/Plonky3#1450 adds pack_columns and pack_columns_fn to PackedValue.
• PackedFieldExtensionExt (pcs/utils.rs) — Partially covered by refactor(field): Add packed field extraction helpers and FieldArray utilities Plonky3/Plonky3#1211. Check whether pack_ext_columns and to_ext_slice are now available upstream; remove what's covered.

Still needs upstream work

• RowMajorMatrixBitrevPackedExt (prover/constraints/packed_row_bitrev.rs) — Extension trait for accessing vertically packed rows from bit-reversed storage. No upstream equivalent.
• horner_acc/horner (pcs/utils.rs) — Generic Horner fold helpers. Could be proposed upstream.

Local cleanup

• log2_strict_u8 — Duplicated in lifted-air/src/util.rs and lmcs/utils.rs. Deduplicate.

---

Ported from 0xMiden/p3-miden#25