feat(talis): add dedicated encoder instances for fibre-txsim

[walldiss]

Summary

• Adds encoder node type to talis for running fibre-txsim on dedicated instances separate from validators
• Each encoder gets its own keyring with unique key prefixes (enc0-*, enc1-*, ...) and independent escrow accounts
• Encoders are round-robin mapped to validators for gRPC and upload shards to all validators
• Frees ~2.5 GB RAM per validator by moving encoding off-box

Changes

• config.go: Encoder NodeType, Encoders []Instance, builder methods
• add.go: --type encoder support
• client.go, google_cloud.go: encoders in Up/Down
• deployment.go: deployEncodersIfConfigured via S3
• genesis.go: encoder payload creation with init script
• network.go: AddEncoder with unique key prefixes
• fibre_setup.go: encoder escrow deposits
• fibre_txsim.go: --on-encoders flag, round-robin validator mapping
• reset.go, txsim.go: encoder cleanup

Test plan

• go build ./tools/talis/ compiles
• talis add -t encoder -c 3 adds encoder instances to config
• talis up + talis deploy creates and deploys to encoder instances
• talis fibre-txsim --on-encoders runs fibre-txsim on encoders
• talis kill-session -s fibre-txsim kills sessions on both validators and encoders
• talis reset cleans up encoder instances

Closes https://linear.app/celestia/issue/PROTOCO-1492/talis-add-dedicated-encoder-instances-for-fibre-txsim

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[ninabarbakadze]

lint is failing

[ninabarbakadze]

utAck