Feat/wpn 1630 use shared serialization

[Julink-eth]

Explanation

Solana, Tron, and Stellar each keep a local { __type, value } serialize/deserialize pair so snap state can round-trip values JSON cannot represent (undefined, BigNumber, bigint, Uint8Array). This PR adds that helper to @metamask/snap-networks-utils so the snaps can share one implementation.

• serialize / deserialize / Serializable are exported from the package.
• Wire format is unchanged: { __type: 'undefined' | 'BigNumber' | 'bigint' | 'Uint8Array', value? }.
• Uint8Array uses portable btoa/atob (same as Tron/Stellar), not Solana’s @solana/kit codec. Encoded bytes still match ([1, 2, 3] → AQID).
  This PR is utils-only. Follow-up PRs will switch Solana, Tron, and Stellar to the shared helpers.

References

• Related to WPN-1630

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

[Copilot]

Pull request overview

Adds shared serialization utilities to @metamask/snap-networks-utils so network snaps can round-trip non-JSON-native values through snap state / interface context using a consistent wire format.

Changes:

• Introduces serialize, deserialize, and Serializable supporting undefined, BigNumber, bigint, and Uint8Array via { __type, value? }.
• Exposes the new helpers from the package root export surface.
• Adds Jest coverage and a changelog entry; introduces needed dependencies (bignumber.js, lodash, @types/lodash).

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
yarn.lock	Adds lockfile entries for newly introduced dependencies.
packages/snap-networks-utils/src/serialization/types.ts	Defines the Serializable type used by the helpers.
packages/snap-networks-utils/src/serialization/serialize.ts	Implements JSON-safe serialization with a stable { __type, value? } wire format.
packages/snap-networks-utils/src/serialization/serialize.test.ts	Adds unit tests covering primitives, nested structures, and Uint8Array encoding.
packages/snap-networks-utils/src/serialization/deserialize.ts	Implements deserialization back to original runtime types.
packages/snap-networks-utils/src/serialization/deserialize.test.ts	Adds unit tests for deserialization, including falsy-value handling and Uint8Array.
packages/snap-networks-utils/src/index.ts	Exports serialize, deserialize, and Serializable from the package entrypoint.
packages/snap-networks-utils/package.json	Adds runtime/dev dependencies required by the new helpers.
packages/snap-networks-utils/CHANGELOG.md	Documents the addition of the new serialization helpers.

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