fix(android): use equals() instead of == for string comparison in Deserializer

[hobostay]

Summary

• Fix key == "null" to "null".equals(key) in Deserializer.java (lines 242, 266)
• The == operator checks reference equality, not value equality
• When strings are deserialized from binary format, they are not interned, so == comparison with the literal "null" would always fail
• This bug causes the null key handling logic to never trigger, potentially leading to incorrect map deserialization

Test plan

• Verify that deserializing a map with a "null" string key correctly pushes a null key to the HippyMap/HippyArray
• Run existing serialization/deserialization unit tests to ensure no regression

🤖 Generated with Claude Code

[tencent-adm]

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[hippy-service]

Hi, @hobostay. Thanks for your PR! 👏

🏷️ You can leave a comment in this PR with #help tag when you need help (e.g. some status checks run failed due to internal issue), admin team members will help asap.

[hippy-service]

After a quick scan, I have approved workflow to run.

Details

• SHA: b7eafe2

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