test, wallet: overhaul wallet_reindex test to wallet_birthtime #34879

The need for this change was ideated during the review of PR 34857.

• The node doesn't need to be restarted (with reindex or without) because rescanblockchain RPC already updates the wallet birthtime, which is the property that needs to be tested - this allows us to rename the test class to highlight the change in intention of the test.
• Generate 9 blocks fewer to fund the miner wallet.
• Generate 30 blocks fewer to accommodate for the wallet scan start time while importing descriptor with "now" timestamp.
• Use common bumpmocktime helper instead of custom advance_time function.
• Unload miner wallet before 20 blocks generation to avoid notifications from being processed by that wallet.
• Change the order of arguments in assert_equal for consistency.
• Add few constant and verbose comments for test clarity.

Note: This overhaul helps in reducing the time taken by the test from 2s to 0s as observed in few runs.

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It appears that this overhaul helps in reducing the tests time as well from 2s to 0s, which is nice to see.

Few runs that I checked: wallet_reindex test time in macOS native job in other PR1 and PR2 - 2 sec. wallet_birthtime test time in macOS native job in this PR - 0 sec.

I’ll take a closer look, but what’s the motivation for those changes?

I’ll take a closer look, but what’s the motivation for those changes?

As mentioned in the last line of the PR description, it started from the review of PR #34857 here: #34857 (review)

Thanks for asking, made me realise that the motivation was obscured away at the end of the PR description. I updated the PR description to highlight the motivation at the start.