refactor: Add Flutter code documentation and resolve `StreamController` warning

[mbfakourii]

Pull Request

• Report security issues confidentially.
• Any contribution is under this license.
• Link this pull request to an issue.

Issue

Closes: #903

Approach

add document and fix bug StreamController

Tasks

• [ ] Add tests
• [ ] Add changes to documentation (guides, repository pages, code comments)

[parse-github-assistant[bot]]

I will reformat the title to use the proper commit message syntax.

[parse-github-assistant[bot]]

Thanks for opening this pull request!

[codecov[bot]]

Codecov Report

Patch coverage: 9.09% and project coverage change: -0.04 :warning:

Comparison is base (d61d704) 38.55% compared to head (0e27c10) 38.51%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #915 +/- ## ========================================== - Coverage 38.55% 38.51% -0.04% ========================================== Files 59 60 +1 Lines 3328 3331 +3 ========================================== Hits 1283 1283 - Misses 2045 2048 +3 ``` | [Impacted Files](https://app.codecov.io/gh/parse-community/Parse-SDK-Flutter/pull/915?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community) | Coverage Δ | | |---|---|---| | [...utter/lib/src/notification/parse\_notification.dart](https://app.codecov.io/gh/parse-community/Parse-SDK-Flutter/pull/915?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-cGFja2FnZXMvZmx1dHRlci9saWIvc3JjL25vdGlmaWNhdGlvbi9wYXJzZV9ub3RpZmljYXRpb24uZGFydA==) | `0.00% <ø> (ø)` | | | [packages/flutter/lib/src/push/parse\_push.dart](https://app.codecov.io/gh/parse-community/Parse-SDK-Flutter/pull/915?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-cGFja2FnZXMvZmx1dHRlci9saWIvc3JjL3B1c2gvcGFyc2VfcHVzaC5kYXJ0) | `0.00% <ø> (ø)` | | | [...utter/lib/src/storage/core\_store\_directory\_io.dart](https://app.codecov.io/gh/parse-community/Parse-SDK-Flutter/pull/915?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-cGFja2FnZXMvZmx1dHRlci9saWIvc3JjL3N0b3JhZ2UvY29yZV9zdG9yZV9kaXJlY3RvcnlfaW8uZGFydA==) | `86.95% <0.00%> (-13.05%)` | :arrow_down: | | [...es/flutter/lib/src/storage/core\_store\_sembast.dart](https://app.codecov.io/gh/parse-community/Parse-SDK-Flutter/pull/915?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-cGFja2FnZXMvZmx1dHRlci9saWIvc3JjL3N0b3JhZ2UvY29yZV9zdG9yZV9zZW1iYXN0LmRhcnQ=) | `0.00% <0.00%> (ø)` | | | [...ackages/flutter/lib/src/utils/parse\_live\_grid.dart](https://app.codecov.io/gh/parse-community/Parse-SDK-Flutter/pull/915?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-cGFja2FnZXMvZmx1dHRlci9saWIvc3JjL3V0aWxzL3BhcnNlX2xpdmVfZ3JpZC5kYXJ0) | `0.00% <ø> (ø)` | | | [...ackages/flutter/lib/src/utils/parse\_live\_list.dart](https://app.codecov.io/gh/parse-community/Parse-SDK-Flutter/pull/915?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-cGFja2FnZXMvZmx1dHRlci9saWIvc3JjL3V0aWxzL3BhcnNlX2xpdmVfbGlzdC5kYXJ0) | `0.00% <ø> (ø)` | | | [packages/flutter/lib/parse\_server\_sdk\_flutter.dart](https://app.codecov.io/gh/parse-community/Parse-SDK-Flutter/pull/915?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-cGFja2FnZXMvZmx1dHRlci9saWIvcGFyc2Vfc2VydmVyX3Nka19mbHV0dGVyLmRhcnQ=) | `20.00% <20.00%> (+11.37%)` | :arrow_up: | | [...lib/src/storage/core\_store\_shared\_preferences.dart](https://app.codecov.io/gh/parse-community/Parse-SDK-Flutter/pull/915?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-cGFja2FnZXMvZmx1dHRlci9saWIvc3JjL3N0b3JhZ2UvY29yZV9zdG9yZV9zaGFyZWRfcHJlZmVyZW5jZXMuZGFydA==) | `12.50% <100.00%> (ø)` | |

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.

[mtrezza]

Is this a bug fix? If so, we'll merge this as fix instead of refactor and just accept the (unrelated?) docs changes in this PR without mentioning them in the changelog.

[mbfakourii]

Is this a bug fix? If so, we'll merge this as fix instead of refactor and just accept the (unrelated?) docs changes in this PR without mentioning them in the changelog.

No, it is a refactor and not a fix. For pub.dev only

[mtrezza]

What does "fix bug StreamController" in the PR title refer to?

[mbfakourii]

What does "fix bug StreamController" in the PR title refer to?

I changed the title. StreamController is just a warning