feat: sessions dx improvements

[joepegler]

PR-Codex overview

This PR updates the SDK version to 4.5.3, adds a new backend URL, and includes token handling improvements.

Detailed summary

• Updated SDK version to 4.5.3
• Added DAN_BACKEND_URL constant
• Improved token handling for npm and secrets
• Updated schema version in biome.json
• Added new wallet client for random account

The following files were skipped due to too many changes: package.json, src/modules/sessions/dan.ts, examples/CREATE_AND_USE_A_SESSION.md, src/modules/utils/Helper.ts, src/modules/utils/Types.ts, src/modules/sessions/abi.ts, src/modules/sessions/sessionSmartAccountClient.ts, src/account/utils/Types.ts, tests/modules/write.test.ts, src/account/BiconomySmartAccountV2.ts

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[github-actions[bot]]

size-limit report 📦

Path	Size
core (esm)	54.93 KB (+1.41% 🔺)
core (cjs)	60.15 KB (+1.4% 🔺)
account (tree-shaking)	52.49 KB (+0.94% 🔺)
bundler (tree-shaking)	2.54 KB (-3.46% 🔽)
paymaster (tree-shaking)	2.23 KB (-4.08% 🔽)
modules (tree-shaking)	40.32 KB (+0.06% 🔺)