Add fastjsonschema, local schemas

[jonhealy1]

Description

• High-Speed Validation Engine: Added new stac-validator fast command for ultra-high performance validation using fastjsonschema.
  • Up to 50x faster execution per object compared to standard jsonschema validation.
  • Persistent Schema Caching: Local disk-based schema cache in local_schemas/.schemas to support offline validation and eliminate network latency.
  • Dynamic Multi-Level Caching: Implements RAM -> Disk -> Network fetch hierarchy for JSON schemas.
  • Robust Fallback: Automated fallback to standard jsonschema for complex schemas that fail to compile under fastjsonschema (e.g., Item Assets extension).
  • Intelligent Output: New summary report including execution metrics (setup time vs. execution time) and consolidated error breakdowns.
  • Added --verbose (-v) and --quiet (-q) support to the fast command for configurable output density.

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Checklist

• Linting: Code is formatted and linted
• Tests: Tests pass. I have included new tests for these changes where applicable.
• Edge Cases: I have manually verified "unhappy paths" and edge cases beyond the basic success criteria (e.g., database connection timeouts, malformed input, strict mapping rejections).
• Documentation: I have updated README.md to reflect any new environment variables, configuration changes, or breaking updates.
• Accountability: I can explain the implementation logic for every line of code submitted.

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[Copilot]

Pull request overview

Adds a new high-performance validation pathway to the STAC Validator CLI by introducing a fast subcommand backed by fastjsonschema and a multi-tier schema caching approach, along with documentation and packaging updates.

Changes:

• Added FastValidator implementation and new stac-validator fast Click command.
• Added a new pytest suite covering basic FastValidator behavior and CLI-output modes.
• Updated packaging/docs/changelog metadata (including a distribution rename and new Dependabot config).

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
stac_validator/fast_validator.py	Implements the fast validation engine, schema fetch/caching, and jsonschema fallback.
stac_validator/stac_validator.py	Registers the new fast Click subcommand and options.
tests/test_fast_validator.py	Adds tests for FastValidator correctness, output modes, and error cases.
pyproject.toml	Adds fastjsonschema, adjusts optional-deps layout, and renames the distribution / adds a second console script.
README.md	Documents the new fast command and updates installation instructions.
CHANGELOG.md	Adds v4.2.0 release notes for the fast validator.
LICENSE	Adds an additional copyright line.
.gitignore	Ignores schema cache artifacts.
.github/dependabot.yml	Introduces Dependabot configuration for pip and GitHub Actions.

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