adjust python test tolerances

[jmalkin]

Expanded test margins for relative accuracy python tests by about 50%, for all provided variants of quantiles sketches.

The original margins are generally ok, but we're using random data in the tests (which also function as documentation/tutorials) and don't have a way to make the structures deterministic even for testing. As a result, we end up with the expected real-world "failures" due to low probability events showing up eventually. We have enough independent tests that it's not surprising that one of them is outside the stated tolerance every so often.

The non-quantiles sketches do not have this issue and are unchanged.

[coveralls]

Pull Request Test Coverage Report for Build 991414770

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 92.76%

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Totals
Change from base Build 991138921:	0.0%
Covered Lines:	2178
Relevant Lines:	2348

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 991414770

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.927%

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Totals
Change from base Build 991138921:	0.0%
Covered Lines:	7415
Relevant Lines:	7572

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💛 - Coveralls