refactor: improve all credentials providers

[yndu13]

You need to complete

• unit tests and/or feature tests
• documentation is changed or added

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.05594% with 30 lines in your changes missing coverage. Please review.

Project coverage is 97.49%. Comparing base (c61dca4) to head (c38bb47).

Files with missing lines	Patch %	Lines
src/Providers/CLIProfileCredentialsProvider.php	75.00%	22 Missing ⚠️
src/Providers/ProfileCredentialsProvider.php	97.67%	2 Missing ⚠️
src/Providers/RamRoleArnCredentialsProvider.php	98.27%	2 Missing ⚠️
src/Credential.php	99.11%	1 Missing ⚠️
src/Providers/DefaultCredentialsProvider.php	98.59%	1 Missing ⚠️
src/Providers/EcsRamRoleCredentialsProvider.php	98.78%	1 Missing ⚠️
...oviders/EnvironmentVariableCredentialsProvider.php	95.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #30      +/-   ##
============================================
- Coverage     98.80%   97.49%   -1.32%     
- Complexity      256      544     +288     
============================================
  Files            24       30       +6     
  Lines           672     1438     +766     
============================================
+ Hits            664     1402     +738     
- Misses            8       36      +28     

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