improve and fix purchase screen components and flow

[radoslavzeman]

• add Valid unit value to TimeSelector
• fix lost params when visiting payment methods modal
• rename time to duration
• add fixed payment button to the bottom of the purchase screen
• other minor improvements and cleanup

[radoslavzeman]

TODO comment about collapsing Chips added back.

Deprecation warning in new expo-router version was fixes by navidation.setOpation() - expo-router issue discussion, new docs PR