test(services): apply mock and naming conventions

[svaloumas]

Description

Since we have adopted some mocking generation and naming conventions after merging this PR, it would be nice to apply those conventions to the rest of the test files to be consistent.
This PR adds some missing constructor tests to the services, renames the test functions accordingly, and replaces the mock files with new ones, generated by make mock.

Motivation and Context

How Has This Been Tested?

Run the tests locally multiple times.

Screenshots / Output (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (no code change)
• Refactor (refactoring production code)
• Other

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-commenter]

Codecov Report

Base: 61.64% // Head: 63.55% // Increases project coverage by +1.91% 🎉

Coverage data is based on head (b8bf94f) compared to base (6ed1684).
Patch coverage: 42.51% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #391      +/-   ##
==========================================
+ Coverage   61.64%   63.55%   +1.91%     
==========================================
  Files          29       30       +1     
  Lines         975     1029      +54     
==========================================
+ Hits          601      654      +53     
+ Misses        322      316       -6     
- Partials       52       59       +7     

Impacted Files	Coverage Δ
service/fcm/fcm.go	90.00% <ø> (+14.00%)	⬆️
service/lark/common.go	100.00% <ø> (ø)
service/plivo/plivo.go	90.38% <ø> (ø)
service/syslog/mock_syslog_writer.go	53.12% <0.00%> (ø)
service/syslog/syslog.go	92.00% <ø> (ø)
service/twilio/twilio.go	92.00% <ø> (+36.00%)	⬆️
service/wechat/mock_wechat_message_manager.go	43.75% <0.00%> (ø)
service/wechat/wechat.go	34.56% <ø> (+19.75%)	⬆️
service/whatsapp/whatsapp.go	22.12% <ø> (+5.30%)	⬆️
service/whatsapp/mock_whatsapp_client.go	18.51% <18.51%> (ø)
... and 11 more

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[nikoksr]

@svaloumas no idea why codecov is complaining. Overall test coverage apparently even increased - let's ignore this. Merge when you're ready.