feat: Allow parsing big number from string value

[AlexV525]

Changes

BigInts were deserialized from num in the code base but serialized to Strings. The type becomes incompatible when a cache layer stores the serialized data and deserializes them when reading from the cache.

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.