purl-next: Validate PURL #43

We need to address the critical issue of validating a PURL, which includes verifying the existence of a PURL and ensuring conformance with the correct PURL syntax.
The work towards this includes updating PurlDB to support on-demand, live queries of upstream package registries and extended syntax and PURL libraries with extended syntax and content validation checks for all the PURL types documented in the PURL specification.
Creating a PURL validation mechanism will further ensure conformance with the PURL specification.

• purl-next: Update FetchCode library for supported ecosystems fetchcode#139
• purl-next: Update the PURL library for Python with extended validation #44
• purl-next: Update PurlDB to support on-demand, live query purldb#643
• purl-next: Extend syntax validation for PURL #47
• purl-next: Create PURL accuracy benchmarks #48