Catch timeout errors for asyncio requests + set timeout value

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 23.07692% with 10 lines in your changes missing coverage. Please review.

Project coverage is 74.13%. Comparing base (87e9a4d) to head (aad8923).

Files	Patch %	Lines
...cializations/stores/nexus/batch_request_handler.py	23.07%	10 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #419 +/- ## ========================================== - Coverage 74.16% 74.13% -0.03% ========================================== Files 106 106 Lines 6974 6979 +5 ========================================== + Hits 5172 5174 +2 - Misses 1802 1805 +3 ``` | [Flag](https://app.codecov.io/gh/BlueBrain/nexus-forge/pull/419/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/BlueBrain/nexus-forge/pull/419/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain) | `74.13% <23.07%> (-0.03%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain#carryforward-flags-in-the-pull-request-comment) to find out more.

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