fix(client): autofill confidential MPT fees

[kpitapeersyst]

fix(client): autofill confidential MPT fees

Description

This PR updates the RPC and WebSocket clients to calculate the required fee for confidential MPT transactions during autofill. Confidential transaction types use ten times the current base fee, while caller-provided fees remain unchanged.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Refactoring

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code where needed
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes

Changes

• Apply a 10x base-fee multiplier to all five confidential MPT transaction types.
• Keep RPC and WebSocket fee calculation behavior aligned.
• Preserve an explicitly provided transaction fee during autofill.
• Add client coverage for fee calculation, fee cushions, and explicit-fee preservation.

Tests

• go test ./xrpl/rpc ./xrpl/websocket

CI status

Note

Lint and Test and Run govulncheck are expected to fail until #345 is merged into confidential-transfers. The target branch already contains the updated mpt-crypto header, but it does not yet contain the matching CGo decryption call added by #345. This PR does not modify confidential/mptcrypto.

After #345 is merged, this branch will be rebased onto the updated target branch and the checks will run again.

Notes

• This PR targets the temporary confidential-transfers integration branch.
• Changelog updates are intentionally deferred until the integration branch stabilizes.