chore: centralize workspace dependencies

[Dzejkop]

Summary

• Centralizes dependency versions and default-feature settings under the root [workspace.dependencies] table.
• Updates every workspace member's normal, development, build, and target-specific dependencies to inherit with workspace = true.
• Keeps crate-specific features and optional flags in the member manifests.
• Aligns shared ciborium and rand version requirements.

Stack

1. chore: replace android cross-rs cross compilation setup with a nix based one #434
2. chore: bump world-id-protocol crates to 0.12 #435
3. This PR

Validation

• cargo check --workspace --all-targets
• Verified every member dependency is inherited from [workspace.dependencies].

---

Note

Low Risk
Manifest-only refactor with no application logic changes; risk is limited to accidental version or feature drift if workspace entries differ from prior per-crate pins.

Overview
Moves shared crate versions and default-features into the root [workspace.dependencies] table and switches walletkit-cli, walletkit-core, walletkit-db, and walletkit-testkit to inherit them with workspace = true across normal, dev, build, and target-specific (wasm32, Android, native) sections.

Member manifests still declare crate-specific features, optional, and target overrides (e.g. Android sha2 force-soft, wasm getrandom). walletkit-core relocates the Android sha2 block into [target.'cfg(target_os = "android")'.dependencies] instead of a trailing package section. Shared pins align ciborium to 0.2.2 and rand to 0.8.6 workspace-wide (including testkit, which previously used 0.8).

^{Reviewed by Cursor Bugbot for commit 25f02b2. Bugbot is set up for automated code reviews on this repo. Configure here.}