Lazy Access to Field Dictionary

[agavra]

Today when we deserialize an ImprintRecord it deserializes the entire field dictionary:

imprint/src/serde.rs

Lines 457 to 467 in 5d921ab

	let mut directory = Vec::new();
	let (count, count_size) = varint::decode(bytes.clone())?;
	bytes.advance(count_size);
	bytes_read += count_size;
	for _ in 0..count {
	let (entry, entry_size) = DirectoryEntry::read(bytes.clone())?;
	bytes.advance(entry_size);
	bytes_read += entry_size;
	directory.push(entry);
	}

Instead, we should just load the bytes into a struct and binary search on that when accessing fields, deserializing (and potentially caching the result) of a field id lookup only when necessary. This is in line with the ethos of Imprint, which optimizes for use cases that only read a few fields in a potentially large field dictionary.

We could consider making this configurable for the use case (eager/lazy deserialization of the field dictionary).