feat(stellar-wallet-snap): use shareable serialization in Stellar snap

[Julink-eth]

Explanation

• Switch the Stellar snap from local serialize / deserialize / Serializable to the shared helpers in @metamask/snap-networks-utils.
• Rewire every call site (snap state, cache, prices, network service) to the shared package.
• Keep serializeToString in src/utils/serialization.ts. It is Stellar-only (request/response logging in BaseHandler) and now wraps the shared serialize. Drop the duplicated serialize/deserialize unit tests; the shared package already covers them. One serializeToString test remains.

References

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

[Julink-eth]

@metamaskbot publish-preview

[github-actions]

Preview builds have been published. Learn how to use preview builds in other projects.

Expand for full list of packages and versions.

@metamask-previews/bitcoin-wallet-snap@2.0.1-preview-e53aa00
@metamask-previews/snap-networks-utils@1.0.0-preview-e53aa00
@metamask-previews/solana-wallet-snap@6.0.0-preview-e53aa00
@metamask-previews/stellar-wallet-snap@0.1.0-preview-e53aa00
@metamask-previews/tron-wallet-snap@3.1.0-preview-e53aa00