Add WalletCore build-only transaction APIs

[3esmit]

🎯 Purpose

Add build-only Wallet APIs for downstream transaction builders. Wallet can now
build public and privacy-preserving transactions without submitting them; the
caller explicitly submits through Wallet. Existing send_* APIs retain their
behavior.

Closes #613

⚙️ Approach

• Add WalletCore::build_pub_tx, build_privacy_preserving_tx, and
  submit_transaction.
• Preserve existing send_* and *_with_pre_check signatures and
  behavior through private build helpers and explicit Wallet submission.
• Add AccountIdentity::account_id() while preserving
  public_account_id().
• Add public and privacy-preserving integration coverage for
  build -> submit -> poll.

🧪 How to Test

Requires Docker Compose v2. Run:

cargo test -p wallet
RISC0_DEV_MODE=1 cargo test -p integration_tests --test wallet_build
cargo clippy -p wallet --all-targets --all-features -- -D warnings

The integration test lets a sequencer block interval pass after each build and
asserts the built hash remains absent. It then explicitly submits the
transaction through Wallet and polls for its result.

🔗 Dependencies

None.

🔜 Future Work

• Integrate these APIs into the downstream transaction-builder work after this
  change has a published commit or release tag.
• Keep CLI adoption and CLI behavior changes in separate follow-up work.

📋 PR Completion Checklist

• Complete PR description
• Implement the core functionality
• Add/update tests
• Add/update documentation and inline comments

[Copilot]

Pull request overview

This PR adds build-only transaction APIs to WalletCore, allowing downstream callers to construct both public and privacy-preserving transactions without submitting them, and to explicitly submit later via a new wallet-owned submission method. It refactors existing send_* and *_with_pre_check methods to preserve their signatures/behavior while delegating through the new build + submit flow, and adds integration coverage for build -> submit -> poll.

Changes:

• Added WalletCore::build_pub_tx, WalletCore::build_privacy_preserving_tx, and WalletCore::submit_transaction, and refactored existing send_* paths to use them.
• Added AccountIdentity::account_id() (keeping public_account_id() intact) plus unit test coverage for all identity variants.
• Added an integration test covering public and privacy-preserving build -> submit -> poll, asserting that build-only does not submit.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
lez/wallet/src/lib.rs	Introduces build-only + submit APIs and refactors existing send APIs to preserve behavior via build-then-submit.
lez/wallet/src/account_manager.rs	Adds AccountIdentity::account_id() and tests projecting IDs across all variants.
integration_tests/tests/wallet_build.rs	Adds integration coverage ensuring build-only doesn’t submit and explicit submission works for both transaction types.

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[3esmit]

I rebased this into dev as required by contribution guidelines. All checks now pass. R
ecommend reviewing the CI run pipeline, as it constantly fails with disk out of space, and it takes way to long due repetitive compiles of nextest.

Consider:

• running all dependencies of nextest under the same CI as separate sub jobs, so nextest is compiled only once;
• and downloading integration test archive only one - so the CI don't runs out of space.