Fix WHERE clause evaluating only first condition

[shurarama]

Fixes #183

Summary

• Bug: matchesConditions() in mem_table/in_mem_select.go returns immediately after evaluating the first WHERE condition, silently ignoring all subsequent AND conditions
• Fix: Use early returns on mismatch — return false when a condition fails, true only after all conditions pass
• Tests: Added two test cases for multi-condition WHERE clauses (match and no-match)

Affected queries

Any query with multiple WHERE conditions on system_schema.* tables, e.g.:

SELECT * FROM system_schema.columns
  WHERE keyspace_name = 'ks' AND table_name = 'tbl';

Previously only keyspace_name was evaluated; table_name was ignored.

Test plan

• Existing tests pass (13/13)
• New test: multiple where conditions — verifies both conditions are applied
• New test: multiple where conditions no match — verifies mismatch on second condition returns no rows
• Verified new tests fail without the fix

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[gemini-code-assist]

Code Review

This pull request updates the matchesConditions function to correctly evaluate multiple WHERE conditions by iterating through all conditions rather than returning after the first one. It also adds unit tests to verify both matching and non-matching scenarios with multiple conditions. A review comment suggests refactoring the logic to use early returns within the switch statement, which would eliminate the need for the matches variable and make the code more idiomatic.

[brandtnewton]

Hi @shurarama, thanks for the contribution! Please squash your commits an use a conventional commit message that starts with fix: and then we should be good to go :)