feat(miden-client): re-export NetworkNotePricer

[huklaa]

Closes #2517.

Summary

• re-export NetworkNotePricer from the miden_client crate root alongside ExecutionOptions
• document the new downstream-visible API in the unreleased changelog
• allow consumers such as miden-faucet to remove their direct miden-tx dependency

Validation

• confirmed NetworkNotePricer is a public root export of the pinned miden-tx dependency
• git diff --check passed
• the available runner does not include Cargo, so hosted CI is the compile/lint gate

Scope check

Immediately before submission, issue comments, open and recently merged PRs, upstream branches, and recent commits were checked. No overlapping implementation was found.