Automate minor version bumps for published Rust crates

### Problem statement

The default branch can retain an `mssql-tds` or `mssql-mock-tds` version that has already been published on crates.io. Starting the next development version currently requires a manual change.

### Proposed solution

Add a scheduled GitHub Actions workflow that checks both crates independently every three UTC days, with a manual trigger as well. When a source version is already published, propose the next minor version and keep the mock crate's versioned local dependency in sync.

Create or reuse a tracking issue for each outstanding bump and create or update one draft PR that closes that issue when merged. Skip unpublished versions, fail explicitly on registry/API errors, and never publish or merge automatically.

### Affected crate

Not applicable / Multiple: `mssql-tds` and `mssql-mock-tds`.

### Alternatives considered

Continue checking crates.io and opening version-bump issues and PRs manually.

### Additional context

Use a daily scheduled trigger with a three-day UTC date check so the cadence does not reset at month boundaries. Document required workflow permissions and the optional automation token needed to trigger downstream GitHub Actions workflows.