[Feature]: Add steam inventory support

[ArtyProf]

Problem Description

No response

Proposed Solution

Cover stamworks API for steam inventory support

Proposed API Design

Feature Category

New Steam API coverage

Related Steam API

Other / New API

Alternatives Considered

No response

Priority

Nice to have

Contribution

• I'm willing to submit a PR for this feature
• I can help test the implementation
• I can help write documentation

Additional Context

No response

[amonguus]

Please do! Great work on the project.