feat: splash screen updates

[justinenerio]

Changes

• remove splash transition during auth loading
• update native splash to gradient background for ios and pre android 12

Checklist

• PR is ready for review (if not, it should be a draft).
• PR title follows Conventional Commits guidelines.
• Screenshots/video added.
• Tests added.
• Self-review done.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9996a42) 81.13% compared to head (6fe7b6e) 81.13%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1201   +/-   ##
=======================================
  Coverage   81.13%   81.13%           
=======================================
  Files         183      183           
  Lines        3939     3939           
=======================================
  Hits         3196     3196           
  Misses        743      743           

Flag	Coverage Δ
solana-beta	81.13% <ø> (?)
solana-stable	81.13% <ø> (ø)

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