feat(schema): Add Culture Context

[logaretm]

Adds Culture context to the schema definitions

relevant to getsentry/sentry-javascript#18801 | PR (getsentry/sentry-javascript#19148)

[Copilot]

Pull request overview

This PR adds a new Culture context to the Relay event schema, which allows capturing cultural and locale-specific information from events. This addition supports the Sentry JavaScript SDK's need to track culture-related information (as referenced in the linked issue and PR).

Changes:

• Added a new CultureContext struct with fields for calendar, display_name, locale, is_24_hour_format, and timezone
• Integrated the Culture context into the Context enum and module system
• Added comprehensive test coverage for the new context
• Updated CHANGELOG to document the feature addition

Reviewed changes

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

File	Description
relay-event-schema/src/protocol/contexts/culture.rs	New file defining the CultureContext struct with fields for cultural/locale information, trait implementations, and roundtrip tests
relay-event-schema/src/protocol/contexts/mod.rs	Added Culture module import/export and Culture variant to the Context enum
CHANGELOG.md	Added entry documenting the Culture context feature

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[Copilot]

The timezone field should be marked with #[metastructure(pii = "maybe")] annotation. This field can potentially contain personally identifiable information similar to how the timezone field in DeviceContext is marked (see relay-event-schema/src/protocol/contexts/device.rs:118-120). Timezone information can reveal user location.

Suggested change

	/// For example, `Europe/Vienna`.
	/// For example, `Europe/Vienna`.
	#[metastructure(pii = "maybe")]

[Copilot]

The display_name field should be marked with #[metastructure(pii = "maybe")] annotation. This field contains human-readable locale information (e.g., "English (United States)") which can reveal user location and preferences, similar to other locale-related fields that are marked as potentially containing PII.

Suggested change

	/// For example, `English (United States)`.
	/// For example, `English (United States)`.
	#[metastructure(pii = "maybe")]

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