fix!: replace dag walkers with generic CID extraction from blocks

[achingbrain]

Replace the codec-specific .dagWalkers property with a generic dag walker internally that uses the Block interface from the multicodecs module.

• Removes the .dagWalkers property from the Helia interface
• Adds getCodec and getHasher to retrieve codecs and hashers by code
• Adds loadCodec and loadHasher options to allow sync or async loading of extra codecs/hashes in addition to staticlly configured ones in the codecs/hashers keys

BREAKING CHANGE: the .dagWalkers property has been removed

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works

[achingbrain]

I think the pinning benchmarks should be re-run with this PR before merging. The multiformats/block .links() function works by deserializing a block into an object, then recursively walking every property and yielding any value that can be turned into a CID.

This could potentially be more expensive than deserializing a block, collecting CIDs during deserialization and then yielding them all as the DAGWalkers do.

[SgtPooki]

a few things that could be changed, not sure if the networked-storage accepting an additional arg was done explicitly for some reason though

[SgtPooki]

we need to run benchmarks to ensure no perf regression

[achingbrain]

Perf seems fine - the benchmark added by #633 shows comparable performance between this branch and main.