* Always activate Canopy at Height(1) on Regtest
* Ignores the zip 212 grace period on configured Testnets and Regtest
* - Returns early when there is no Heartwood activation height when creating or updating HistoryTree
- Skips call to `check::legacy_chain()` when no NU5 activation height is set (it would return immediately anyway)
- Replaces `.map()` with `.filter_map()` in `NetworkUpgrade::target_spacings()`
- Removes outdated TODO
* - When proof of work is disabled, skips checking if Zebra is synced to the network tip in the getblocktemplate method
* Sets full_verifier_utxo_lookahead to Height::MIN instead of panicking
* When network is regtest, skips starting sync task and commits the genesis block if it's missing in the state
* updates/fixes test config
* Adds test for committing Canopy blocks on Regtest
* - Updates median time past and difficulty checks to use fewer than 11/17/28 blocks
* uses SLOW_START_INTERVAL of 0 if PoW is disabled, adds TODOs
* Update getblocktemplate method to return reserved chain history activation root hash, uses Nu5 at height 1
Test passes.
* Updates test to expect NU5 as the default nu activation at Height(1)
* Removes invalid difficulty snapshot
* fixes tests
* removes regtest NU5 activation height config field
* Apply suggestions from code review
* Update zebra-state/src/service/check/difficulty.rs
Co-authored-by: Marek <mail@marek.onl>
* Update zebra-state/src/service/check/difficulty.rs
* Updates docs/comments, renames an argument
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Co-authored-by: Marek <mail@marek.onl>
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