feat(frontend): Integrate backend user transactions in Solana scheduler and services

[AntonioVentilii]

Motivation

The Solana user transaction services and utilities were introduced in #12220 and #12221, but the scheduler (SolWalletScheduler) and the transaction loading service (loadSolTransactions) did not yet use them.

This PR wires the backend persistence layer into both, matching the pattern already established for EVM in eth-transactions.services.ts.

Changes

• sol-wallet.scheduler.ts: On initial sync (isInitialSync), load stored transactions from the backend via loadSolUserTransactions and seed the internal store. Save newly discovered RPC transactions back to the backend via saveSolFinalizedTransactions (fire-and-forget with error logging via consoleError).
• sol-transactions.services.ts: In the private loadSolTransactions, load stored transactions from the backend and merge them with fresh RPC results. Save new RPC transactions back to the backend. Both operations are gated behind USER_TRANSACTIONS_LOAD_FROM_BACKEND_ENABLED.

Tests

Added tests.

[Copilot]

Pull request overview

Integrates Solana backend user-transaction persistence into the Solana wallet scheduler and Solana transaction loading service, aligning behavior with the existing EVM pattern.

Changes:

• Load stored Solana user transactions from the backend and merge/seed them into frontend stores.
• Save newly discovered finalized Solana transactions back to the backend (fire-and-forget with error logging).
• Add/extend unit tests for scheduler and services backend integration behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
src/frontend/src/sol/services/sol-transactions.services.ts	Loads stored backend transactions and saves new RPC transactions, gated by USER_TRANSACTIONS_LOAD_FROM_BACKEND_ENABLED.
src/frontend/src/sol/schedulers/sol-wallet.scheduler.ts	Seeds scheduler’s internal transaction store from backend on initial sync and saves newly found RPC transactions.
src/frontend/src/tests/sol/services/sol-transactions.services.spec.ts	Adds tests asserting backend load/merge/save behavior for Sol transaction services.
src/frontend/src/tests/sol/schedulers/sol-wallet.scheduler.spec.ts	Adds tests asserting backend load-on-initial-sync and save-on-new-RPC behavior for the wallet scheduler.

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