fix: support optional backtrace fields and types

[joshuap]

• allow string and int types for backtrace number field
• add missing optional backtrace field types
• coerce number/column fields to int instead of string

Fixes #8

[Copilot]

Pull Request Overview

This PR fixes backtrace field handling by adding support for flexible number field types and missing optional fields. The changes ensure the API can properly unmarshal backtrace data that may contain numbers as either strings or integers.

• Introduces a custom Number type that handles both string and integer JSON values
• Adds missing optional backtrace fields (column, class, type, args)
• Updates the Number field in BacktraceEntry to use the new flexible type

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
internal/hbapi/types.go	Adds custom Number type with flexible JSON unmarshaling and updates BacktraceEntry with missing optional fields
internal/hbapi/types_test.go	Comprehensive test coverage for Number unmarshaling and BacktraceEntry with all field variations