[Feature] Make subscribe_blocks return header

[mattsse]

Component

rpc

Describe the feature you would like

currently:

alloy/crates/provider/src/provider/trait.rs

Line 802 in b227b17

) -> TransportResult<alloy_pubsub::Subscription<N::BlockResponse>> {

returns blocks, this is misleading because this subscription only emits headers.

this only works because all the fields are serde default:

alloy/crates/rpc-types-eth/src/block.rs

Lines 25 to 40 in b227b17

	/// Uncles' hashes.
	#[cfg_attr(feature = "serde", serde(default))]
	pub uncles: Vec<B256>,
	/// Block Transactions. In the case of an uncle block, this field is not included in RPC
	/// responses, and when deserialized, it will be set to [BlockTransactions::Uncle].
	#[cfg_attr(
	feature = "serde",
	serde(
	default = "BlockTransactions::uncle",
	skip_serializing_if = "BlockTransactions::is_uncle"
	)
	)]
	pub transactions: BlockTransactions<T>,
	/// Withdrawals in the block.
	#[cfg_attr(feature = "serde", serde(default, skip_serializing_if = "Option::is_none"))]
	pub withdrawals: Option<Withdrawals>,

Additional context

No response