Migrate from deprecated Edalize Tool API to the Flow API

[keegandent]

Problem

When running with the most recent version of Edalize, the following warning is displayed

This backend is deprecated and will eventually be removed. Please migrate to the flow API instead. See https://edalize.readthedocs.io/en/latest/ref/migrations.html#migrating-from-the-tool-api-to-the-flow-api for more details.

Proposed Solution

Modify the configurations in /fpga/config/targets.json, schema documentation in /fpga/config/README.md, and code in /fpga/_processor.py to utilize the Edalize flow API.

Hurdles

There may be potential differences in the new EDA flow logic that affect how repeat runs are handled. Solutions should try to preserve the current "lazy" policy of not re-running synthesis and implementation for networks with valid bitstreams.

Expected API Impacts

No software or hardware API changes are expected.