Update complex_adaptor to match precision requirements.

[jzmaddock]

Add test case. Fixes https://github.com/boostorg/multiprecision/issues/595

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (de24099) 94.1% compared to head (d9bb0dd) 94.1%.

Additional details and impacted files

[](https://app.codecov.io/gh/boostorg/multiprecision/pull/597?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) ```diff @@ Coverage Diff @@ ## develop #597 +/- ## ======================================= Coverage 94.1% 94.1% ======================================= Files 273 273 Lines 28525 28525 ======================================= Hits 26834 26834 Misses 1691 1691 ``` | [Files](https://app.codecov.io/gh/boostorg/multiprecision/pull/597?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) | Coverage Δ | | |---|---|---| | [include/boost/multiprecision/complex\_adaptor.hpp](https://app.codecov.io/gh/boostorg/multiprecision/pull/597?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg#diff-aW5jbHVkZS9ib29zdC9tdWx0aXByZWNpc2lvbi9jb21wbGV4X2FkYXB0b3IuaHBw) | `89.5% <ø> (ø)` | | ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/boostorg/multiprecision/pull/597?src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/boostorg/multiprecision/pull/597?src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). Last update [de24099...d9bb0dd](https://app.codecov.io/gh/boostorg/multiprecision/pull/597?src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg).