Transition to OpChainSpec for Optimism node

[mattsse]

we're currently still using the unified chainspec type:

reth/crates/optimism/cli/src/chainspec.rs

Lines 25 to 30 in 20d6950

	/// Optimism chain specification parser.
	#[derive(Debug, Clone, Default)]
	pub struct OpChainSpecParser;
	impl ChainSpecParser for OpChainSpecParser {
	type ChainSpec = ChainSpec;

this should be OpChainSpec instead, this also means we need to get rid of all remaining

ChainSpecParser<ChainSpec = ChainSpec>

and

ChainSpecProvider<ChainSpec = ChainSpec>

in favor of trait restrictions