Add support of Maker rebate activity type

[codez0mb1e]

Changelog:

• Fix Activity model missing MAKER_REBATE type from Polymarket API #40
• Introduce ActivityType alias to avoid copy-paste of literals.

[Copilot]

Pull request overview

This PR fixes a ValidationError that occurred when the Polymarket API returned activities with a MAKER_REBATE type, which was not included in the Activity model's type literal. It also introduces a reusable ActivityType alias to eliminate duplication of the literal values.

Changes:

• Added MAKER_REBATE to the accepted activity types and created an ActivityType type alias to centralize the literal definition
• Replaced the duplicated inline Literal[...] in get_activity()'s type parameter with the new ActivityType alias
• Bumped package version from 0.5.0 to 0.5.1

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/polymarket_apis/types/data_types.py	Introduced ActivityType alias with MAKER_REBATE added, and used it in the Activity model
src/polymarket_apis/types/__init__.py	Exported ActivityType in imports and __all__
src/polymarket_apis/clients/data_client.py	Imported ActivityType and replaced inline literal duplication in get_activity()
pyproject.toml	Version bump from 0.5.0 to 0.5.1

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