fix(tapd): fix panic when casting fields

[d4x1]

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Summary

What does this PR do?
Fix panic when casting fields in tapd.

In tapd, some datas are like:

"field_changes":
        [
            {
                "field": "secret_root_id",
                "field_label": "label_name",
                "value_after":
                {
                    "allow_list": "dw;1234;dw",
                    "secret_root_id": "1156232825001092299",
                    "participant_fields": "1"
                },
                "value_before":
                {
                    "allow_list": "",
                    "secret_root_id": 0,
                    "participant_fields": "0"
                },
                "secret_root_id": "1234",
                "value_after_parsed":
                {
                    "allow_list": "dw;123;dw",
                    "secret_root_id": "12345",
                    "participant_fields": "1"
                },
                "value_before_parsed":
                {
                    "allow_list": "",
                    "secret_root_id": "0",
                    "participant_fields": "0"
                }
            }
        ]

Field participant_fields can be float or string type depending on its location. This PR just handles these cases.

Does this close any open issues?

Closes N/A

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