[AP-2998] Handle Decimal objects in format_messages

[amofakhar]

Description of change

Context

Because the new version uses orjson, it does not handle decimal objects in the message.
This update adds a handler for decimal objects and convert them to float.

https://transferwise.atlassian.net/browse/AP-2998

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[Copilot]

Pull request overview

Changes: Bugfix (1), Maintenance (1)

This PR addresses a serialization gap introduced by using orjson: decimal.Decimal values inside Singer messages couldn’t be serialized. It adds an orjson default handler for decimals and bumps the package version / changelog for the release.

Changes:

• Add an orjson.dumps(..., default=...) handler to convert decimal.Decimal values to float during message formatting.
• Bump package version to 3.0.2.
• Document the change in CHANGELOG.md.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
singer/messages.py	Adds a Decimal handler and wires it into format_message’s orjson.dumps call.
setup.py	Bumps package version to 3.0.2.
CHANGELOG.md	Adds a 3.0.2 entry describing the Decimal handling change.

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