feat: provider client 1:n binding support

[Kavindu-Dodan]

This PR

A follow up PR to introduce 1:N support - Check diff from main

Fixes and completes #186

A follow-up for the PR #188

This PR brings,

• 1 to N binding of provider (a single provider to multiple client binding capability)
• completes eventing specification by adding API-level events for success/error initialization
• Improves the eventing implementation and adds more tests

[codecov]

Codecov Report

Merging #190 (c69a27c) into main (220dc33) will increase coverage by 1.92%.
The diff coverage is 97.51%.

❗ Current head c69a27c differs from pull request most recent head 337536c. Consider uploading reports for the commit 337536c to get more accurate results

@@            Coverage Diff             @@
##             main     #190      +/-   ##
==========================================
+ Coverage   77.03%   78.95%   +1.92%     
==========================================
  Files           9        9              
  Lines         997     1074      +77     
==========================================
+ Hits          768      848      +80     
+ Misses        207      204       -3     
  Partials       22       22              

Impacted Files	Coverage Δ
pkg/openfeature/provider.go	65.38% <0.00%> (-2.62%)	⬇️
pkg/openfeature/event_executor.go	98.71% <98.14%> (+2.37%)	⬆️
pkg/openfeature/api.go	92.41% <100.00%> (+2.32%)	⬆️
pkg/openfeature/openfeature.go	97.67% <100.00%> (ø)

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[toddbaert]

This is great. I don't see any issues from a spec perspective. The testing is very robust. I had a nit about some of the tests here, but if this is more effort than it's worth I'm fine with leaving it as is, though perhaps with a comment we're testing a private API as a proxy for a public one.

[RealAnna]

LGTM!