refactor(toolkit): give each ledger version its own copy of the builders

[ozgb]

Overview

Last of three PRs closing #1768: directories compiled twice via Rust's
#[path = "…"] attribute, once bound to the ledger-8 crates and once to the
ledger-9 crates, so that super:: resolves differently in each instantiation.
A reader of such a file cannot tell which ledger crate an alias refers to, and
an edit meant for one generation silently applies to both. #2059 fixed
ledger/src/, the previous PR in the stack fixed ledger/helpers/src/, and
this one fixes the two remaining occurrences in the toolkit.

Both used the same trick:

#[path = "common"]
#[allow(clippy::duplicate_mod)]
pub mod inner {
    pub use midnight_node_ledger_helpers::ledger_8 as ledger_helpers_local;
    pub mod batch_single_tx; mod batches; … pub mod type_convert;
}
pub use inner::*;

so builders/common/ (16 files, 3328 lines) and commands/fork/common/
(8 files, 374 lines) were each compiled twice. Each version now has its own
directory — builders/{ledger_8,ledger_9}/ and
commands/fork/{ledger_8,ledger_9}/ — and each file names its own version with
one use midnight_node_ledger_helpers::ledger_N as ledger_helpers_local; line,
so bodies stay byte-identical between the two copies.

util/toolkit/src/commands/common/ is a different, single-compiled module and
is left alone.

This is not a move toward a generic <L: Ledger> builder. rustc already
emitted both instantiations; this only makes the existing duplication visible so
diff -r can police it. In particular type_convert.rs's identity conversions
on the v9 side stay exactly as they are.

Notes for review:

• The inner wrapper module disappears. It is referenced nowhere outside these
  four files, so every external path (builders::ledger_8::SingleTxBuilder,
  fork::ledger_9::show_wallet, …) and the whole CLI surface are unchanged.
• impl_encoded_zswap_conversions! stays in builders/mod.rs. Its comment
  needed one phrase updated, but the reason still holds: ledger_storage
  aliases to ledger_storage_ledger_8 in both versions, so some types are
  shared and duplicate impls would still conflict with E0119.
• remote_prover.rs (impl …ledger_8::ProofProvider) is outside the duplicated
  tree and is untouched.

With this merged, grep -rn '#\[path' --include='*.rs' over the workspace
returns nothing and no directory is compiled more than once — #1768 is done.

🗹 TODO before merging

• Ready
• Merges after the ledger-helpers PR it is based on.

📌 Submission Checklist

• All commits are signed off (git commit -s) for the DCO
• Changes are backward-compatible (or flagged if breaking)
• Pull request description explains why the change is needed
• Self-reviewed the diff
• I have included a change file, or skipped for this reason:
• If the changes introduce a new feature, I have bumped the node minor version
• Update documentation (if relevant)
• Updated AGENTS.md if build commands, architecture, or workflows changed
• No new todos introduced

🧪 Testing Evidence

$ cargo test -p midnight-node-toolkit
test result: ok. 135 passed; 0 failed; 1 ignored

(The Docker-based hardfork_e2e integration test fails locally against a stale
pre-#2059 node image — expected header tag 'midnight:ledger-state[v18]:', got '…[v13]:' from the container's own genesis load, before any toolkit code runs.
CI builds that image from the branch.)

The layout check the split buys — the two copies must be identical apart from
the version name:

$ diff -r builders/ledger_8 builders/ledger_9      # normalised: s/ledger_[89]/ledger_N/
DIFFERS: mod.rs                                     # the per-version serialize_tx
$ diff -r commands/fork/ledger_8 commands/fork/ledger_9
(identical)

And the surface is unchanged:

$ cargo run -p midnight-node-toolkit -- --help      # same commands as before
$ grep -rn '#\[path' --include='*.rs' ledger util node pallets primitives runtime   # no hits
$ grep -rn 'duplicate_mod' --include='*.rs' .                                       # no hits

Also run: cargo fmt --all --check, cargo clippy -p midnight-node-toolkit --all-targets -- -D warnings, cargo check --workspace --all-targets,
cargo build --release.

• Additional tests are provided (if possible)

🔱 Fork Strategy

• N/A — toolkit only, no runtime or client behaviour change.

Links

• Closes Remove shared common modules to isolate ledger-version behavior #1768

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[chatgpt-codex-connector]

Add the required license headers to new Rust files

Add LICENSE_HEADER.txt to this newly introduced source file and the other headerless additions: seven command files under each ledger version, plus contract_custom.rs, register_dust_address.rs, and transactions.rs under each builders version. All 20 are added as new .rs paths in this commit but begin directly with imports, contrary to the repository requirement for every new source file.

AGENTS.md reference: AGENTS.md:L239-L241

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