add getPath method as a generator that returns blocks for the targeted dag and all blocks traversed while resolving a cid+path string

supports carScope to specify what blocks to return for the resolved dag
- 'all': return the entire dag starting at path. (default)
- 'block': return the block identified by the path.
- 'file': Mimic gateway semantics: Return All blocks for a multi-block file or just enough blocks to enumerate a dir/map but not the dir contents.

see: storacha/freeway#33
see: storacha/freeway#34

TODO:
- [] find out how to identify the boundaries of a unixfs hamt (unixfs-exported seems to define it as "not having an empty or null Link.Name after the first 2 chars are stripped, which seems risky... what happens if the actual dir listing has 2 char long link names? see: https://github.com/ipfs/js-ipfs-unixfs/blob/e853049bd63d6773442e1540ae49b6a443ca8672/packages/ipfs-unixfs-exporter/src/resolvers/unixfs-v1/content/hamt-sharded-directory.ts#L20-L42

License: MIT
Signed-off-by: Oli Evans <oli@protocol.ai>

License: MIT
Signed-off-by: Oli Evans <oli@protocol.ai>

License: MIT
Signed-off-by: Oli Evans <oli@protocol.ai>

License: MIT
Signed-off-by: Oli Evans <oli@protocol.ai>

License: MIT
Signed-off-by: Oli Evans <oli@protocol.ai>

License: MIT
Signed-off-by: Oli Evans <oli@protocol.ai>

License: MIT
Signed-off-by: Oli Evans <oli@protocol.ai>

License: MIT
Signed-off-by: Oli Evans <oli@protocol.ai>

License: MIT
Signed-off-by: Oli Evans <oli@protocol.ai>

Co-authored-by: Alan Shaw <alan.shaw@protocol.ai>