feat(signer): load keys in parallel

[ltitanb]

speed up keys loading at startup by parallezing decryption across cores

[Copilot]

Pull Request Overview

This PR parallelizes key loading by leveraging Rayon for concurrent decryption and updates dependency versions and workspace settings.

• Added rayon and jsonwebtoken as workspace dependencies in signer and common crates
• Refactored load_from_* functions to collect directory entries and decrypt in parallel
• Updated eth2_keystore dependency in root Cargo.toml to use a Git tag instead of a specific revision

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 2 comments.

File	Description
crates/signer/Cargo.toml	Added jsonwebtoken workspace entry
crates/common/src/signer/loader.rs	Refactored sequential loops to parallel iterations with Rayon
crates/common/Cargo.toml	Added jsonwebtoken and rayon workspace entries
Cargo.toml	Changed eth2_keystore from a git revision to a git tag and added rayon dependency

Comments suppressed due to low confidence (2)

crates/common/src/signer/loader.rs:112

• Parallel loading paths introduce concurrency concerns. Add unit or integration tests to verify correct behavior across different directory structures and error cases.

fn load_from_lighthouse_format(

Cargo.toml:39

• Pinning to a moving Git tag can undermine reproducible builds. Consider using a specific commit SHA for deterministic dependency resolution.

eth2_keystore = { git = "https://github.com/sigp/lighthouse", tag = "v7.0.1" }