Modularize Phase1 into post-Merge features: Sharding, Custody Game, Data Availability Sampling

[protolambda]

This takes the older phase1 PRs #2146 and #2172 and rebases it onto dev (including the new Merge)

Progress:

• Rebase DAS PR by @vbuterin onto latest The-Merge work
• Rebase out clutter (generated files and such) that got into the old DAS PR
• Clean up old shard code, remove ShardTransition accounting in favor of independent shard blobs.
• Remove legacy light client design in favor of new Altair design.
• Split custody game, DAS, and base sharding docs
• Remove old phase1 pyspec building
• Refactor custody game logic out of sharding, implement as extension instead.
• Update block processing and epoch processing to call Altair and Merge-fork processing functions, not just phase0
  • blocked by merge work, waiting for that branch to adopt Altair changes. rebase of Merge in Altair in future PRs, use phase0 for now.
• Update BeaconState type in sharding spec to support Merge.
• Update DAS spec to implement discv5.1 based long-range sample method (for Future PR maybe?)
• Clean up old phase1 references in testing
• Retain proof of custody testing (no proof of custody executable spec, tests are being skipped for now)
• Ratain start-shard unit tests (no sharding executable spec, tests are being skipped for now)
• Drop shard-transition tests in favor of new data-availability focused shards (no strict transitions, just data linked into beacon chain)
• Update block processing and epoch processing helpers with missing merge/sharding/proof-of-custody methods, dropping shard-transition related processing.
• Add phase naming for SHARDING, CUSTODY_GAME, DAS to tag tests with (to be enabled later). Note: custody tests need more in-depth updates, as the sharding design changed.
• Update Makefile to drop older phase1 work
• Drop old phase1 configs, split into new feature configs.
• Update README

The bigger picture of this PR is to accelerate sharding after the merge, and enable early testnets to have shard-data, while DAS and proof of custody continue to be developed. Features, not phases.

[hwwhww]

And:

• Fix test generators. There are some from eth2spec.test.context import PHASE1 in testgen main.pys.

🙏

[djrtwo]

lots of minor formatting and link fixes