Feat (proxy): flag to enable/disable QT return

[Giuseppe5]

Reason for this PR

Considering we cache quant metadata during export, we do not need to propagate QuantTensors during export.
This will come in handy for future features, including lazy dequantization which assumes a different paradigm in inference vs export.

Changes Made in this PR

Return a normal tensor from proxies during export.
Set all return_quant_tensor to False during tracing, and restore their states immediately after.

Testing Summary

NA

Risk Highlight

• This PR includes code from another work (please detail).
• This PR contains API-breaking changes.
• This PR depends on work in another PR (please provide links/details).
• This PR introduces new dependencies (please detail).
• There are coverage gaps not covered by tests.
• Documentation updates required in subsequent PR.

Checklist

• Code comments added to any hard-to-understand areas, if applicable.
• Changes generate no new warnings.
• Updated any relevant tests, if applicable.
• No conflicts with destination dev branch.
• I reviewed my own code changes.
• Initial CI/CD passing.
• 1+ reviews given, and any review issues addressed and approved.
• Post-review full CI/CD passing.

[nickfraser]

See the comment. If you think this is the best approach then approved - please merge (after FINN integration is fixed!)