Make tree settings configurable

[mattsse]

currently we rely on constants for certain tree settings

reth/crates/engine/tree/src/tree.rs

Lines 52 to 58 in c4bf5bb

	/// Maximum number of blocks to be kept only in memory without triggering persistence.
	const PERSISTENCE_THRESHOLD: u64 = 256;
	/// Number of pending blocks that cannot be executed due to missing parent and
	/// are kept in cache.
	const DEFAULT_BLOCK_BUFFER_LIMIT: u32 = 256;
	/// Number of invalid headers to keep in cache.
	const DEFAULT_MAX_INVALID_HEADER_CACHE_LENGTH: u32 = 256;

it would be useful to have a way to configure these easily, we already have a way to configure certain values:

reth/crates/engine/tree/src/tree.rs

Lines 261 to 262 in c4bf5bb

	block_buffer_limit: u32,
	max_invalid_header_cache_length: u32,

reth/crates/engine/tree/src/tree.rs

Lines 445 to 447 in c4bf5bb

	let state = EngineApiTreeState::new(
	DEFAULT_BLOCK_BUFFER_LIMIT,
	DEFAULT_MAX_INVALID_HEADER_CACHE_LENGTH,

TODO

• introduce a treeconfig type that has these as fields, and defaults are the constants