Print duration needed to reach assume_valid_target in the Header Sync phase.

[eval-exec]

• Add DEFAULT_ASSUME_VALID_TARGET_HEIGHT to calculate duration need to reach the target
• Print duration to reach assume_valid_target in log msg

What problem does this PR solve?

This PR let CKB print duration needed to reach to DEFAULT_ASSUME_VALID_TARGET in log

2024-04-28 06:12:02.343 +00:00 BlockDownload INFO ckb_sync::synchronizer  best known header number: 8760000, hash: Byte32(0x323b52e2309b15bb5d1bc0e3497da2905b14e2014313e1d01c8cea816b55e361), CKB is reaching the assume valid target: Byte32(0xc394fa4c5e5032c49f3502d4fd8054ead76ff693a54ac90757e441b5119afcaf) Please wait. It will take about 7.7 minutes to reach the assume valid target
2024-04-28 06:12:03.727 +00:00 BlockDownload INFO ckb_sync::synchronizer  best known header number: 8770000, hash: Byte32(0xd383dacd15a1db0b746f1af2c20b845cc89222485f975a4084990c74da6904af), CKB is reaching the assume valid target: Byte32(0xc394fa4c5e5032c49f3502d4fd8054ead76ff693a54ac90757e441b5119afcaf) Please wait. It will take about 7.6 minutes to reach the assume valid target
2024-04-28 06:12:05.104 +00:00 BlockDownload INFO ckb_sync::synchronizer  best known header number: 8780000, hash: Byte32(0x1e16b3079422c122acd30eaef0525a17f9828be5a3ceba79c72e9c7d69b75245), CKB is reaching the assume valid target: Byte32(0xc394fa4c5e5032c49f3502d4fd8054ead76ff693a54ac90757e441b5119afcaf) Please wait. It will take about 7.5 minutes to reach the assume valid target

https://github.com/nervosnetwork/ckb/pull/4254#issuecomment-1840263490

print duration need to reach DEFAULT_ASSUME_VALID_TARGET in Header Sync phase

If ckb run is specified with a custom --assume-valid-target, the corresponding height of this target is not known temporarily, so it is currently not possible to calculate the time needed to reach this target.

Related changes

• print duration need to reach DEFAULT_ASSUME_VALID_TARGET in Header Sync phase

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code ci-runs-only: [ quick_checks,linters ]

Side effects

• None

Release note

None: Exclude this PR from the release note.

[eval-exec]

Propose a new approach: Calculate Header Sync progress and "time remaining to sync to the highest tip Header" using the timestamps of the genesis block and the latest tip header.