feat: add text field weights support to TextQuery (#360)

[bsbodden]

Adds the ability to specify weights for text fields in RedisVL queries, enabling users to prioritize certain fields over others in search results.

• Support dictionary of field:weight mappings in TextQuery constructor
• Maintain backward compatibility with single string field names
• Add set_field_weights() method for dynamic weight updates
• Generate proper Redis query syntax with weight modifiers
• Comprehensive validation for positive numeric weights

Example usage:

# Single field with weight
query = TextQuery(text="search", text_field_name={"title": 5.0})

# Multiple fields with weights
query = TextQuery(
    text="search",
    text_field_name={"title": 3.0, "content": 1.5, "tags": 1.0}
)