feat(l1): implement flatCallTracer

[azteca1998]

Summary

• Add flatCallTracer tracer type for debug_traceTransaction and block tracing endpoints
• Returns a flat array of call frames following the Parity/OpenEthereum trace format
• Each frame includes traceAddress (position in call tree as array of indices) and subtraces (direct child count)
• Uses the action/result sub-object structure: action.callType, action.from, action.to, etc.
• Supports frame types: "call", "create", and "suicide"
• Implemented by post-processing the existing call tracer output (depth-first recursive flattening)

Closes part of #6572

[github-actions]

⚠️ Known Issues — intentionally skipped tests

Source: docs/known_issues.md

Known Issues

Tests intentionally excluded from CI. Source of truth for the Known
Issues section the L1 workflow appends to each ef-tests job summary
and posts as a sticky PR comment.

EF Tests — Stateless coverage narrowed to EIP-8025 optional-proofs

make -C tooling/ef_tests/blockchain test calls test-stateless-zkevm
instead of test-stateless. The zkevm@v0.3.3 fixtures are filled against
bal@v5.6.1, out of sync with current bal spec; the broad target trips ~549
fixtures. Re-broaden once the zkevm bundle is regenerated.

Why and resolution path

PR #6527 broadened
test-stateless to extract the entire for_amsterdam/ tree from the
zkevm bundle and run all of it under --features stateless; combined with
this branch's bal-devnet-7 semantics that scope produces ~549
GasUsedMismatch / ReceiptsRootMismatch /
BlockAccessListHashMismatch failures.

test-stateless-zkevm filters cargo to the eip8025_optional_proofs
suite, which still validates the stateless harness without the bal-version
mismatch.

Re-broaden by switching test: back to test-stateless in
tooling/ef_tests/blockchain/Makefile once the zkevm bundle is regenerated
against the current bal spec.

[github-actions]

Lines of code report

Total lines added: 255
Total lines removed: 0
Total lines changed: 255

Detailed view

+-----------------------------------------+-------+------+
| File                                    | Lines | Diff |
+-----------------------------------------+-------+------+
| ethrex/crates/networking/rpc/tracing.rs | 570   | +255 |
+-----------------------------------------+-------+------+