* Remove redundant documentation
The documentation was exactly the same as the documentation from the
trait.
* Calculate a mock time block delta for tests
Simulate a block being added to the chain with a random block time based
on the previous block time and the target spacing time.
* Add a `time` field to `ChainTipBlock`
Store the block time so that it's ready for a future chain that allows
obtaining the chain tip's block time.
* Add `ChainTip::best_tip_block_time` method
Allow obtaining the bes chain tip's block time.
* Add method to obtain both height and block time
Prevent any data races by returning both values so that they refer to
the same chain tip.
* Add `NetworkUpgrade::all_target_spacings` method
Returns all the target spacings defined for a network.
* Create a `NetworkChainTipEstimator` helper type
Isolate the code to calculate the height estimation in a new type, so
that it's easier to understand and doesn't decrease the readability of
the `chain_tip.rs` file.
* Add `ChainTip::estimate_network_chain_tip_height`
This is more of an extension method than a trait method. It uses the
`NetworkChainTipHeightEstimator` to actually perform the estimation, but
obtains the initial information from the current best chain tip.
* Fix typo in documentation
There was an extra closing bracket in the summary line.
* Refactor `MockChainTipSender` into a separate type
Prepare to allow mocking the block time of the best tip as well as the
block height.
* Allow sending mock best tip block times
Add a separate `watch` channel to send the best tip block times from a
`MockChainTipSender` to a `MockChainTip`.
The `best_tip_height_and_block_time` implementation will only return a
value if there's a height and a block time value for the best tip.
* Fix off-by-one height estimation error
Use Euclidean division to force the division result to round down
instead of rounding towards zero. This fixes an off-by-one error when
estimating a height that is lower than the current height, because the
fractionary result was being discarded, and it should have forced the
height to go one block back.
* Fix panics on local times very far in the past
Detect situations that might cause the block height estimate to
underflow, and return the genesis height instead.
* Fix another off-by-one height estimation error
The implementation of `chrono::Duration::num_seconds` adds one to the
number of seconds if it's negative. This breaks the division
calculation, so it has to be compensated for.
* Test network chain tip height estimation
Generate pairs of block heights and check that it's possible to estimate
the larger height from the smaller height and a displaced time
difference.
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