fix no-std dependency graph and add regression CI

[yapishu]

Fixes the merged no-std dependency regression by removing an unused unconditional tracing dependency that pulled once_cell/std into bare-metal builds.

Adds a regression workflow for pushes to master, pull requests, and manual runs. It verifies:

• a real bare-metal thumbv7em-none-eabihf build of the production no-std library;
• the no-default-feature test suite, including the secret-dependent Schnorr nonce regression and canonical Hoon KAT;
• the hosted test suite and Hoon parity integration tests.

Validated locally from a clean worktree with all three workflow commands. The fixed dependency commit also builds successfully as part of the optimized xtensa-esp32s3-none-elf nockster firmware with chip security enabled.