ci: add weekly automated Cargo.lock update workflow

[SH20RAJ]

Adds a scheduled workflow to refresh Cargo.lock weekly and open a PR only when lockfile changes are detected.

Highlights:

• schedule: every Monday 06:00 UTC
• manual trigger via workflow_dispatch
• runs cargo update with fresh resolution
• no direct commits to main
• opens PR using peter-evans/create-pull-request with dependencies label
• concurrency guard to prevent overlapping runs

Closes #1044

[SH20RAJ]

Hi! Added a weekly automated Cargo.lock update workflow. This ensures that the project's dependencies are kept up-to-date and that we catch any breaking dependency updates early. (Fixes #1044)

[SH20RAJ]

Addressing Issue #1044. This PR adds an automated workflow to refresh Cargo.lock weekly. By keeping dependencies up-to-date and opening PRs for lockfile changes, we ensure that security patches and minor version improvements are integrated regularly, reducing the risk of 'dependency rot'. 🔄