Add ActiveSupport Supports

[Watson1978]

Related to #111

Problem

Currently, the code uses JSON.generate(msg) in JSON fallback. This forces a standard JSON serialization, potentially ignoring custom serialization logic defined within the objects themselves.

Solution

Change the implementation to use msg.to_json.
JSON.parse(msg.to_json).to_msgpack

This allows objects to control their own string representation via their to_json method before being parsed back into a Hash for MessagePack conversion.

Context & Benefits

This change ensures that if an object has a custom to_json implementation, it is respected.

Example: Active Support (Rails)
A major beneficiary of this change is environments where Active Support is loaded.
In Active Support, to_json delegates to as_json, which handles:

• Non-standard objects (like Symbols, specific class instances).
• Date/Time formatting (e.g., ISO 8601).
• Custom logic defined in models.

By using msg.to_json, we ensure that logs forwarded by fluent-logger-ruby match the expected JSON format defined by the application/framework, rather than the raw internal representation.

[daipom]

Thanks!

Since the Active Support topic suddenly appears, it’s a bit hard to follow, so I’d like to clarify the purpose of this PR.
My understanding is that #111 is not directly related to Active Support itself, but it would be more convenient to align with the JSON format definition provided by Active Support.

This improvement would be useful. Looks good to me.

However, it seems a part of #111 is still unresolved.
I’m particularly concerned about how the timestamps of the Flunetd Event itself are handled.
In particular, when using nanosecond_precision, I’m concerned about what happens to the milliseconds of the Event’s timestamp if a JSON fallback occurs.

fluent-logger-ruby/lib/fluent/logger/fluent_logger.rb

Lines 49 to 51 in 6bcebac

	def to_json(*args)
	@sec.to_s
	end

It seems that #111 should remain open.

[daipom]

It seems we should leave a comment on why we need this.

[Watson1978]

Added a comment.
ec11c6d

[daipom]

Since the Active Support topic suddenly appears, it’s a bit hard to follow, so I’d like to clarify the purpose of this PR.

The title change has made it much clearer. Thanks!

[Watson1978]

In particular, when using nanosecond_precision, I’m concerned about what happens to the milliseconds of the Event’s timestamp if a JSON fallback occurs.

Even with nanosecond_precision enabled, EventTime's nsec values seem to be truncated when JSON fallback occurs.

[Watson1978]

Since the Active Support topic suddenly appears, it’s a bit hard to follow, so I’d like to clarify the purpose of this PR.
My understanding is that #111 is not directly related to Active Support itself, but it would be more convenient to align with the JSON format definition provided by Active Support.

The primary purpose of this PR is to respect the object's own to_json implementation instead of forcing JSON.generate. This allows any Ruby object (not just in Rails) to control its own JSON serialization format.

Active Support is just the most prominent use case where to_json behavior differs significantly from JSON.generate. I will update the description to clarify that the main goal is generic to_json support, with Active Support cited as a key example.

[daipom]

Thanks!