feat(data-processing): contributor activity timeline builder (#876)

[CodeMayor]

Closes #876

Changes

• Enhanced contributor_activity_timeline.py with dict + object support, project_id filter, case-insensitive contributor matching, and extended action categories (milestone, withdrawal)
• Added get_contributor_activity_timeline() to PostgresService — queries contract_events table with parameterised SQL (no injection risk), sorted newest-first
• Added Alembic migration 1810000000000 for composite index on (contributor, timestamp DESC) for fast timeline queries
• Expanded test suite with 15+ unit + integration tests covering all acceptance criteria

Acceptance Criteria

• Supports contributor-centric timeline queries (contributor + project_id filters)
• Includes timestamps and action categories (deposit, contribution, registry, milestone, withdrawal, other)
• Backed by testnet event data (queries contract_events table)
• Output consumable by backend or frontend APIs (/contributors/{contributor}/timeline endpoint, returns clean JSON)

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[Cedarich]

@CodeMayor

[CodeMayor]

@CodeMayor

@Cedarich thanks for the tag — did you have feedback or questions about this PR?

[Cedarich]

Yes please fix the failing CI

[CodeMayor]

sorry, i saw the message late but i've later worked on the CI.

[Cedarich]

@CodeMayor