Port celestia-app-fibre contents to celestia-app

[rootulp]

Context

https://github.com/celestiaorg/celestia-app-fibre was used to develop Fibre.

Problem

We don't want to maintain a fork of celestia-app long term.

Proposal

After these PRs merge:

1. feat!: prep for app version 8 #6620
2. chore(deps): upgrade go-square from v3 to v4.0.0-rc2 #6624

We should port the celestia-app-fibre contents to celestia-app. At a minimum this involves:

• x/fibre
• x/valaddr
• the new message type for PayForFibre
• the square construction changes