fix: do not panic on constructor param errors

[barjin]

Introduces better error handling for constructor parameter errors.

Closes #280

[Copilot]

Pull Request Overview

This PR improves error handling in constructor parameters by replacing panics with proper Result returns. The core change propagates errors from the build() method instead of using unwrap(), preventing runtime panics when client construction fails.

Key Changes:

• Modified ImpitBuilder::build() to return Result<Impit, ImpitError> instead of Impit
• Enhanced error messages to include contextual information (URLs, proxy configurations)
• Updated all language bindings (Python, Node.js) to handle the new error-returning API

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
impit/src/impit.rs	Changed build() return type to Result, propagated errors from new_reqwest_client(), added proxy error handling
impit/src/errors.rs	Enhanced UrlParsingError to include the URL string, added From<reqwest::Error> implementation
impit-python/src/errors.rs	Updated pattern matching for new UrlParsingError(String) variant
impit-python/src/client.rs	Added error handling for build() result in synchronous client
impit-python/src/async_client.rs	Added error handling for build() result in async client
impit-node/src/lib.rs	Added error handling and mapping for build() result in Node.js binding

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