Support real-pays-fee through three proxy levels

[edpoptart]

Description

Extends ChargeTransactionPaymentWrapper fee-payer resolution for RealPaysFee proxy calls to support a bounded proxy chain of up to three proxy levels.

This also supports homogeneous batch, batch_all, and force_batch calls at the innermost supported level, while preserving the existing fallback where batches containing mixed real accounts are charged to the original signer.

The transaction priority behavior remains unchanged.

Related Issue(s)

• N/A

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Breaking Change

N/A

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run ./scripts/fix_rust.sh to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Screenshots (if applicable)

N/A

Additional Notes

Validation performed:

• ./scripts/fix_rust.sh completed cargo check, cargo clippy --fix, cargo fix, and cargo fmt
• cargo test -p node-subtensor-runtime --test transaction_payment_wrapper passed with 25 tests.
• git diff --check passed.

The failing checks appear unrelated to this change:

• cargo audit is failing on existing yanked dependencies (core2 0.4.0, keccak 0.1.5).
• Try Runtime / check testnet fails in migrate_fix_total_issuance_evm_fees with TotalIssuance diff greater than allowable delta; finney and devnet passed.
• Validate-Benchmarks generated the standard benchmark patch artifact and suggests applying the apply-benchmark-patch label.

This PR only changes ChargeTransactionPaymentWrapper fee-payer resolution/tests/docs and does not touch dependencies, migrations, or pallet benchmarked extrinsics.