feat(evm): single-dimension gas repricing primitives (1/3)

[davidtaikocha]

What

Foundational, pure additive primitives for a future Taiko fork that folds proving cost into a single repriced gas dimension — the eventual replacement for the current Unzen raw_gas × multiplier zk-gas meter. This is the first of three PRs:

1. This PR — primitives (no wiring, no behavior change)
2. Fork wiring + gating — introduce the new TaikoSpecId, wire these into the factory/handler, and gate the difficulty/zk-gas path to end at the new fork (proving cost then commits via the standard gasUsed)
3. Teardown of the Unzen zk-gas subsystem once Unzen retires

Scope / safety

• Not wired into execution. Nothing calls this code yet; every existing fork (including Unzen) behaves identically. The only change outside the new module is one pub mod gas_reprice; line.
• Numbers are non-consensus placeholders. Real opcode/precompile/intrinsic values are a separate calibration effort and must be mirrored in taiko-geth + the prover.
• All 45 evm-crate tests pass (8 new + 37 existing, including every zk_gas test — confirming zero behavior change).

The primitives (crates/evm/src/gas_reprice/)

• schedule.rs — RepriceSchedule { opcode_surcharge: [u64; 256], tx_intrinsic_surcharge }.
• opcodes.rs — repriced_instruction_table: an additive static_gas surcharge over revm's spec base table (the same mechanism revm itself uses for EIP-150/2929), charged before the opcode body so OOG, the GAS opcode, and 63/64 call-forwarding stay self-consistent. No revm fork required.
• precompiles.rs — apply_precompile_surcharge: an input-scaled gas surcharge via PrecompilesMap::map_precompile (mutates only gas_used, forwards everything else).
• intrinsic.rs — add_tx_intrinsic_surcharge: a per-transaction intrinsic addition (covers ecrecover proving) with the same over-limit check revm raises.

Notes for the wiring PR

• The opcode→fn pairings in opcodes.rs duplicate revm's internal table (because Instruction::static_gas is private) — re-audit them on every reth/revm pin bump (documented in-code).
• Only a small example opcode set is wired; a surcharge on an unwired opcode is silently ignored by design (documented on the field + pinned by a test).
• floor_gas (EIP-7623 calldata floor) is intentionally untouched by the intrinsic surcharge.
• Precompile OOG is carried via PrecompileOutput.status, not always as Err — the wiring layer owns gas-limit re-validation.

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