Add string extraction utilities for parsing structured text

[NewGraphEnvironment]

Summary

Add utility functions for extracting text segments from strings using regex patterns.

Functions

• ngr_str_extract_between() - Extract text between two regex delimiters from a character vector
• ngr_str_df_extract() - Apply multiple regex extractions to a data frame column, creating new columns for each segment

Use Case

Parsing semi-structured text like grant descriptions where fields are separated by labels:

"Grant Amount: $400,000 Intake Year: 2025 Region: Fraser Basin"

Features

• Case-insensitive matching
• Optional whitespace normalization (squish)
• Handles optional colons after labels
• Named list input creates correspondingly named output columns