Add support for parsing .npmrc filesAdd npmrc parser

[Shaurya-dev7]

Adds support for parsing .npmrc configuration files.

Implemented NpmRcHandler and registered it for package datafile discovery. Parsed values are stored in extra_data while preserving raw config values.

The parser:

• ignores comments and malformed lines
• supports duplicate keys with last-value-wins behavior
• handles array syntax (key[]=value)
• preserves values containing multiple = characters
• keeps scoped registries and env variable references as raw strings

Added tests and fixtures covering common .npmrc patterns and edge cases.

Fixes #4494