chore(js-ts): Convert utility files to TypeScript (9 files)

[devin-ai-integration]

Summary

Converts 9 utility files from JavaScript to TypeScript as part of the ongoing JS→TS migration (Playbook 6 — Utility Functions).

Batch 1 (5 files):

• app/util/walletconnect.js → .ts — pure exports, type inference sufficient
• app/util/payment-link-generator.js → .ts — add string parameter/return types
• app/util/device/index.js → .ts — Device class, add async return type
• app/util/confirm-tx.js → .ts — add types to all gas/currency helper functions
• app/util/ENSUtils.js → .ts — add types, replace this.ens with module-level variable, add CacheEntry interface

Batch 2 (4 files):

• app/util/gasUtils.js → .ts — pure BigNumber constants, type inference sufficient
• app/util/general/index.js → .ts — add types to all general utility functions, define NavigationRoute interface
• app/util/custom-gas/index.js → .ts — add types to gas calculation functions
• app/util/conversions.js → .ts — add types to all hex/wei/gwei conversion functions, fix .js import extension

No logic changes — types only.

Review & Testing Checklist for Human

• Verify ENSUtils.ts change from this.ens to module-level ensInstance variable preserves the same runtime behavior (the original used this in free functions which would have been the module scope)
• Verify general/index.ts timeoutFetch Promise.race return type is compatible with callers
• Spot-check that parameter types match actual usage (especially confirm-tx.ts where some params could be number | string)

Notes

• walletconnect.ts and gasUtils.ts needed zero changes — TypeScript infers their types correctly from the literal/constructor values
• The ENSUtils.ts change from this.ens to a module-level variable is a minor structural improvement — the original code used this in exported free functions which referred to the module object at runtime

Link to Devin session: https://app.devin.ai/sessions/51734166b8b740daa75579e47f5a94be
Requested by: @lukepage-COG

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