callstack: Add case to handle nestable instant events

[theibhir]

What it does

Show markers for nestable instant events

How to test

• run the incubator
• load the following trace:

{
"traceEvents": [
{
"name": "HandleRequest",
"cat": "server",
"ph": "B",
"ts": 1000000,
"pid": 1,
"tid": 10,
"args": {
"endpoint": "/api/user"
}
},
{
"name": "ParseJSON",
"cat": "server",
"ph": "B",
"ts": 1000100,
"pid": 1,
"tid": 10
},
{
"name": "json_parse_step",
"cat": "parser",
"ph": "n",
"ts": 1000120,
"pid": 1,
"tid": 10,
"id": "0xabc",
"args": {
"key": "user_id",
"value_type": "string"
}
},
{
"name": "ParseJSON",
"cat": "server",
"ph": "E",
"ts": 1000300,
"pid": 1,
"tid": 10
},
{
"name": "QueryDatabase",
"cat": "database",
"ph": "B",
"ts": 1000400,
"pid": 1,
"tid": 10,
"args": {
"query": "SELECT * FROM users WHERE id=?"
}
},
{
"name": "QueryDatabase",
"cat": "database",
"ph": "E",
"ts": 1000800,
"pid": 1,
"tid": 10
},
{
"name": "HandleRequest",
"cat": "server",
"ph": "E",
"ts": 1001000,
"pid": 1,
"tid": 10
}
]

}

Follow-ups

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the instructions in this template

[arfio]

Thank you for the PR, I reviewed and approve the changes (even though I forgot to press review)