fix(tests): align pytest coverage docs with required setup (#1259)

[chethanuk]

Summary

• document pytest-cov in the test README dependencies
• keep the coverage command scoped to the intended Python test directories and preserve verbose output
• address review feedback so the README matches actual pytest collection behavior

Validation

• verified README diff is scoped to tests/README.md
• confirmed documented install command includes pytest-cov
• confirmed coverage command is scoped to tests/client tests/server tests/session tests/vectordb tests/misc tests/integration with term-missing output

Closes #1259

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PR Reviewer Guide 🔍

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🎫 Ticket compliance analysis ✅ 1259 - Fully compliant Compliant requirements: Fix the error when running test scripts due to unrecognized --cov arguments Align test documentation with required setup

⏱️ Estimated effort to review: 1 🔵⚪⚪⚪⚪

🏅 Score: 100

🧪 No relevant tests

🔒 No security concerns identified

✅ No TODO sections

🔀 No multiple PR themes

⚡ No major issues detected

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