Fix escaped single quote handling in FakeEmbeddings filter comparison

[Copilot]

The FakeEmbeddings test fixture regex correctly extracts SQL-escaped single quotes ('') from filter expressions but wasn't unescaping them before comparison, causing false negatives for metadata values containing apostrophes.

Changes:

• Unescape filter values in tests/utils.py by replacing '' → ' before comparison
• Add test coverage for single quotes, multiple quotes, and baseline cases

Example:

# SQL query built by TxtaiStore._build_sql escapes quotes
sql = "SELECT * FROM txtai WHERE [author] = 'O''Brien'"

# Before: raw_val = "O''Brien" didn't match stored value "O'Brien"
# After: expected = raw_val.replace("''", "'") matches correctly

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