test: add unit tests for contribarena.models.tool_results Pydantic models

[northline-lab]

Summary

Add focused unit tests for contribarena.models.tool_results Pydantic models that previously had no dedicated test coverage.

Models now tested

Model	Purpose
CommandType	Literal type alias for command categories (verification, setup, discovery, other)
CommandResult	Captures shell command execution results with stdout/stderr/exit code
PatchResult	Records patch application success/failure and modified files
PatchOperation	Represents a single file operation (create, update, move, delete)
AciResult	ACI tool execution result with error/recovery metadata
AgentStep	Single agent loop step with phase, tool, state, duration
RepoMetadata	Repository metadata from GitHub API (stars, forks, language)
IssueCandidate	GitHub issue with number, title, labels, timestamps
PullRequestCandidate	GitHub PR with state, author, draft flag, linked issues
IssueLinkage	Issue assignees, linked PRs, and recent comments
RepoSetupProbeResult	Repository setup probe outcome with package managers and CI
RepoReadmeResult	Repository README fetch result with content and path
EligibilityResult	Repository eligibility check with reasons, warnings, checks

Test Coverage

• CommandTypeLiteralTest (2 tests) — literal values pinned, invalid value rejected via ValidationError
• CommandResultTest (5 tests) — required fields, defaults, explicit values, all literal values accepted
• PatchResultTest (4 tests) — required fields, defaults, explicit values, factory independence
• PatchOperationTest (3 tests) — required fields, defaults, explicit values
• AciResultTest (4 tests) — required fields, defaults, explicit values, factory independence
• AgentStepTest (3 tests) — required fields, defaults, explicit values
• RepoMetadataTest (3 tests) — required fields, defaults, explicit values
• IssueCandidateTest (4 tests) — required fields, defaults, explicit values, factory independence
• PullRequestCandidateTest (5 tests) — required fields, defaults, explicit values, factory independence for labels and linked_issues
• IssueLinkageTest (6 tests) — required fields, defaults, explicit values with nested PRs, factory independence
• RepoSetupProbeResultTest (7 tests) — required fields, defaults, explicit values, factory independence for 3 list fields
• RepoReadmeResultTest (4 tests) — required fields, defaults, explicit values, unsuccessful result with error
• EligibilityResultTest (5 tests) — required fields, defaults, explicit values, factory independence
• ToolResultsImportTest (1 test) — all 12 symbols importable from models package

No production code is modified.

Verification

• pytest -q tests/unit/test_tool_results_models.py → 61 passed in 0.22s
• ruff check tests/unit/test_tool_results_models.py → All checks passed
• No secrets in diff

Risk

Low — test-only addition. No production code is modified.

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Prepared by ContribArena in owned-live mode.