Add phpstan-phpunit and phpstan-strict-rules

[phil-davis]

1. added phpstan-phpunit and phpstan-strict-rules to composer.json and fixed up things reported about test code.
2. Add phpstan messages to ignoreErrors instead of ignoring
3. fixup things reported in real code

[codecov]

Codecov Report

Merging #105 (496e883) into master (2626b72) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #105   +/-   ##
=========================================
  Coverage     99.73%   99.73%           
  Complexity      109      109           
=========================================
  Files             7        7           
  Lines           376      376           
=========================================
  Hits            375      375           
  Misses            1        1           

Impacted Files	Coverage Δ
lib/EmitterTrait.php	100.00% <ø> (ø)
lib/Loop/Loop.php	100.00% <100.00%> (ø)
lib/Loop/functions.php	100.00% <100.00%> (ø)
lib/Promise.php	100.00% <100.00%> (ø)
lib/Promise/functions.php	100.00% <100.00%> (ø)

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[staabm]

it might make sense to configure phpstan with treatPhpDocTypesAsCertain: false since we have defensive code which makes double sure that types in phpdocs are really passed as expected

[phil-davis]

I tried that locally, and it does not make any difference for this message.
Somehow PHPstan "knows" about Promises and Generator and still thinks that the check can never fail.

For now, IMO we can just keep this in ignoreErrors

[phil-davis]

@staabm please review again and merge if you think it looks OK.

IMO the code changes I made are just being more explicit in "if" statements - phpstan now wants all "if" conditions to be real booleans. No more just saying if($var) when $var is not actually boolean type.

[staabm]

thank you

[phil-davis]

I am getting back to a backlog of sabre-io issues and PRs - there should be some action from now and over the coming weekend.