feat(evm): add native precompile runtime base

[phenix3443]

What

Subtask 1 of the precompile → cosmos/evm native-mode migration: add x/evm/precompiles/base, a thin shared runtime skeleton over cosmos/evm's precompiles/common. This lets moca precompiles stop hand-rolling GetCacheContext / Snapshot / RevertToSnapshot / commit templates (currently duplicated across all 11) and share one snapshot / gas-metering / balance-sync implementation.

API (base.Precompile)

Embeds cosmos/evm's common.Precompile + the precompile ABI:

• RunPrecompile(evm, contract, readonly, exec) — rejects native value up front (moca precompiles are not payable), then delegates to RunNativeAction (the official snapshot / gas / balance-handler model, which converts action errors into EVM reverts).
• Dispatch(contract, readonly, isTx) — pass-through to SetupABI: method dispatch by ID, read-only write protection, argument unpacking.
• WithBalanceHandler(bankKeeper) — opt-in BalanceHandlerFactory for state-changing precompiles that move native balances.

Intended per-precompile usage:

func (c *Contract) Run(evm, contract, readonly) ([]byte, error) {
	return c.RunPrecompile(evm, contract, readonly, c.Execute)
}
func (c *Contract) Execute(ctx, evm, contract, readonly) ([]byte, error) {
	method, args, err := c.Dispatch(contract, readonly, c.IsTransaction)
	...switch method.Name...
}

Design notes

• Execute signature: the plan doc wrote Execute(ctx, stateDB, contract, readonly), but moca handlers emit logs via evm (evm.StateDB.AddLog), matching cosmos/evm's own precompiles which pass the EVM, not the StateDB. So ExecuteFn takes evm (StateDB is reachable via evm.StateDB).
• Gas: empty KvGasConfig (like cosmos/evm's own precompiles); moca keeps charging a flat per-method cost via each precompile's RequiredGas, so the base must not double-charge store gas.
• RejectValue is kept as the mandatory pre-check (migration decision 1).

Tests

Helper-level unit tests (no EVM needed): constructor wiring (address / empty gas / balance-handler opt-in) and Dispatch behavior (routes tx/query methods, unpacks args, rejects tx methods in read-only calls). The full runtime path (RunPrecompile → RunNativeAction) is exercised end-to-end by the bank migration (subtask 2), which runs through EvmKeeper.CallEVMWithData.

• No existing precompile is migrated here (additive only).
• go test ./x/evm/precompiles/base -count=1 → ok.
• Base branch is precompile-integration.