feat!: Add Textual SignModeHandler

[amaury1093]

Description

Closes: #13700
Closes: #13747

This PR adds:

• a new sign mode handler for Textual
• all client-side and ledger-side infrastructure to make it work

Depends on:

• feat!: Add SIGN_MODE_TEXTUAL ledger-cosmos-go#39

---

Author Checklist

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[amaury1093]

This was mainly an exploration PR to make the e2e flow work. I'll close this PR, and divide it into 2 separate ones:

1. one solely for add the SignModeHandler: feat: Add Textual SignModeHandler #14650
2. another one for client-side infra: CLI flags, keyring, ledger support, and tests (tracked by Allow client-side signing with SIGN_MODE_TEXTUAL  #13747(