Investigating on the size of Source types

[h-a-n-a]

RawSource contains two variants:

• Buffer
• Source

Buffer was required to convert to String to satisfy trait Source. With the signature sign of stream_chunks, string converted from RawSource::Buffer needs to be stored on the RawSource to get a satisfying lifetime. Most of the used variant of RawSource is String, so this would add extra 40-byte size overhead for creating RawSource::String (64-byte RawSource, String only takes 24 bytes)

I'm here to propose splitting RawSource into two types: RawStringSource and RawBufferSource.

(on 64-bit machine)

[h-a-n-a]

Cached Source types like CachedSource creates a copy of the original data.

For type RawSource which was wrapped by CachedSource would contain two copies of raw data.
This just probably does not make any sense for caching source code or any other source code types.

I don't know if we can remove source cache from intermediate source types. Consider of this scenario:

OriginalSource -> ReplaceSource -> CachedSource -> ConcatSource -> CachedSource.

This would create three copies of code and the first CachedSource contains source code that is an intermediate result. Maybe we should cache the last one(OriginalSource and edits and cache are stored) or we just give up on caching source code(only OriginalSource and edits are stored).

[h-a-n-a]

Fixed #144