Refactor data readers

[Tigrov]

• Refactor DataReader class
• Rename DataReader to PdoDataReader class
• Refactor BatchQueryResult
• Use DataReaderInterface as a result of method Query::each()

As a result ->rewind() can be called multiple times before iteration. It allows to get access to the first row before iteration.

Related PR

• Refactor data readers db-mssql#300

Q	A
Is bugfix?	✔️/❌
New feature?	❌
Breaks BC?	✔️
Fixed issues	#821, #716

[codecov]

Codecov Report

Attention: Patch coverage is 88.63636% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 99.41%. Comparing base (e380ae2) to head (884e9c7).

Files	Patch %	Lines
src/Query/BatchQueryResult.php	85.71%	3 Missing ⚠️
src/Driver/Pdo/PdoDataReader.php	88.88%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #822      +/-   ##
============================================
- Coverage     99.56%   99.41%   -0.16%     
+ Complexity     1316     1311       -5     
============================================
  Files            64       64              
  Lines          3236     3228       -8     
============================================
- Hits           3222     3209      -13     
- Misses           14       19       +5     

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