Upgrade Rust toolchain to 1.94+ and unpin sqlx-cli

[alejandro-runner]

Problem

CI uses Rust 1.93.0 but sqlx-cli 0.9.0 now requires Rust 1.94.0+. We pinned sqlx-cli@0.8.3 as a workaround, but staying on an older toolchain accumulates drift and blocks future dependency upgrades.

What's needed

• Update Rust toolchain to 1.94+ in both CI workflows (build-test-push-synvya.yaml, build-test-push.yaml)
• Update Rust version in the Dockerfile to match
• Remove the @0.8.3 pin from cargo install sqlx-cli in both workflows
• Build locally with the new toolchain and verify no new compiler warnings surface under RUSTFLAGS: -D warnings
• Check whether other Synvya repos share these workflows and need the same bump

Effort: small

References

Pinned in commit 21e4331