## Issue Addressed
N/A
## Proposed Changes
https://github.com/sigp/lighthouse/pull/3133 changed the rpc type limits to be fork aware i.e. if our current fork based on wall clock slot is Altair, then we apply only altair rpc type limits. This is a bug because phase0 blocks can still be sent over rpc and phase 0 block minimum size is smaller than altair block minimum size. So a phase0 block with `size < SIGNED_BEACON_BLOCK_ALTAIR_MIN` will return an `InvalidData` error as it doesn't pass the rpc types bound check.
This error can be seen when we try syncing pre-altair blocks with size smaller than `SIGNED_BEACON_BLOCK_ALTAIR_MIN`.
This PR fixes the issue by also accounting for forks earlier than current_fork in the rpc limits calculation in the `rpc_block_limits_by_fork` function. I decided to hardcode the limits in the function because that seemed simpler than calculating previous forks based on current fork and doing a min across forks. Adding a new fork variant is simple and can the limits can be easily checked in a review.
Adds unit tests and modifies the syncing simulator to check the syncing from across fork boundaries.
The syncing simulator's block 1 would always be of phase 0 minimum size (404 bytes) which is smaller than altair min block size (since block 1 contains no attestations).
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