♻️ uniformize with other sdks

[sebastianMindee]

Description

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Requires a change to the official Guide documentation.

[Copilot]

Pull request overview

This PR aims to “uniformize with other SDKs” by expanding Ruby SDK parity around polling cancellation, FieldConfidence comparison helpers, and stricter URL input validation (SSRF hardening), along with corresponding RBS and spec updates.

Changes:

• Add Mindee::HTTP::CancellationToken and wire it into V1/V2 async polling methods.
• Add SSRF-focused URL validation to URLInputSource (scheme/credentials/loopback/DNS-resolved IP range checks) plus extensive specs.
• Extend FieldConfidence with </> operators and named aliases, updating RBS and adding specs.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
Steepfile	Adds stdlib stubs (ipaddr, resolv) needed by new SSRF logic.
lib/mindee/http.rb	Requires the new cancellation token implementation.
lib/mindee/http/cancellation_token.rb	Introduces a cancellation token used by polling logic.
sig/mindee/http/cancellation_token.rbs	Adds RBS signature for the cancellation token.
lib/mindee/v2/client.rb	Adds optional cancellation token support to async polling.
lib/mindee/v1/client.rb	Adds optional cancellation token support to async polling.
lib/mindee/input/sources/url_input_source.rb	Adds SSRF validation for URL inputs.
sig/mindee/input/sources/url_input_source.rbs	Updates URLInputSource RBS for new validation helpers/constants.
spec/input/sources/url_input_source_spec.rb	Adds test coverage for the new SSRF URL validation rules.
lib/mindee/v2/parsing/field/field_confidence.rb	Adds </> and named aliases on FieldConfidence.
sig/mindee/v2/parsing/field/field_confidence.rbs	Updates RBS to reflect new FieldConfidence methods.
spec/v2/parsing/field_confidence_spec.rb	Adds tests for new FieldConfidence comparisons/aliases.
spec/http/cancellation_token_spec.rb	Adds tests for CancellationToken behavior.
spec/v2/client_v2_spec.rb	Adds tests for cancellation token behavior in V2 polling.
spec/v1/client_spec.rb	Adds tests for cancellation token behavior in V1 polling.