Fix parse error on flow containers containing child flow containers

[fktn-k]

This PR has fixed parse errors on flow style containers which contains child flow style containers like the following valid JSON-like YAML snippet:

{
  "a": [
    "foo",
    "bar"
  ],
  "b": [
    [
      true,
      false
    ],
    [
      123,
      456
    ]
  ]
}

The root cause is that the fkYAML deserializer didn't properly handle nested flow style container prefix events.
To validate the fix, the test suite has also been updated by adding several test cases for the deserialization feature.

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• Changes are described in the pull request or in a referenced issue.
• The test suite compiles and runs without any error.
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[github-actions]

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[coveralls]

Pull Request Test Coverage Report for Build 9148221027

Details

• 16 of 16 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 9147143461:	0.0%
Covered Lines:	3752
Relevant Lines:	3752

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