feat(keyring-eth-hd): add keyring v2 getters

[ccharly]

Re-expose the same getters than the v1 (inner) keyring, so we can use v2 keyrings to replace their current usage.

---

Note

Medium Risk
Adds new public accessors that expose sensitive key material (mnemonic/seed/HD keys) through the v2 wrapper; while pass-through, it can broaden where secrets are accessed and relied upon.

Overview
Re-exposes legacy HD keyring state on the v2 HdKeyring wrapper by adding passthrough getters for mnemonic, seed, root, hdWallet, and hdPath (returning undefined pre-deserialization) to maintain compatibility with v1 consumers.

Adds unit tests asserting the getters mirror the inner keyring values and updates the changelog to document the new API surface.

^{Reviewed by Cursor Bugbot for commit c56bb3b. Bugbot is set up for automated code reviews on this repo. Configure here.}

[mathieuartu]

LGTM! Worth scanning if we'd need to do this for other types of V2 keyrings as well. But this PR can be merged regardless!