Add unit tests for server tools

[Copilot]

Following PR #3's model tests, this adds unit tests for the 6 server tools (search_sites, get_site_context, search_devices, get_device_context, read_blueprint, get_historical_telemetry).

Changes

New test file: tests/unit/mcp/test_server.py (16 tests, 785 LOC)

• Pagination: Tests offset/limit behavior across search_sites, search_devices, read_blueprint
• Regex filtering: Name and timezone pattern matching
• Context generation: Site statistics (device counts, gateway detection) and device context (connectivity, properties, telemetry, blueprint)
• Blueprint sections: Properties, telemetry, alerts with pattern filtering
• Historical telemetry: Time-series retrieval with granularity

Test structure

class TestServerSearchSites:
    async def test_search_sites_basic(self) -> None:
    async def test_search_sites_pagination(self) -> None:
    # ... pattern filtering tests

class TestServerGetDeviceContext:
    async def test_get_device_context(self) -> None:
        # Validates connectivity, properties, telemetry, blueprint

Uses AsyncMock for HTTP client mocking and a custom MockAsyncStream for API response streams.

Coverage: 86% server.py, 96% overall (29 total unit tests)

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