Client chunking default params

[alanshaw]

We're considering a change to the default chunking parameters that will more closely reflect the defaults chosen by Lotus:

Current IPFS defaults:

• Chunk size: 262144
• Max links: 174

Lotus defaults:

• Chunk size: 1048576
• Max links: 1024

Why?

• 🟢 Flatter DAGs
• 🟢 Fewer things to announce to the DHT
• 🟡 Same CIDs for the same content vs Lotus different hash functions (see below)
• 🟡 Different CIDs for the same content vs IPFS (although IPFS still stuck in v0 so we have that problem anyway since we use v1)
• 🔴 Less de-duping

UPDATE:

Thanks to @vasco we know that blake2js is way slower than sha256. It is not surprising because sha256 uses native webcrypto in the browser and Node.js crypto module. There is an npm module with native bindings for Node.js and a module with a WASM version of blake as well. The work to integrate and test this would be huge and there's no benchmark data for either module so it might not even be faster than the native sha256 versions. Unless there are objections I vote we stick with sha256 hashing for now but switch chunk size and max children.