feat(literature): implement Europe PMC adapter, literature MCP tools, and CLI (v0.7.0)

[engkinandatama]

Summary of Changes

• Schema Models: Added PublicationEntity and LiteratureContext in src/biocontext/schemas.py with full citation metadata (PMID, PMCID, DOI, title, authors, journal, year, abstract text, citation count, open access URL).
• Literature Adapter: Implemented LiteratureAdapter in src/biocontext/adapters.py connecting to the Europe PMC REST API (https://www.ebi.ac.uk/europepmc/webservices/rest/search), supporting search by topic/gene symbol, canonical PubMed ID (EXT_ID:<pmid> AND SRC:MED), PMCID, and DOI.
• EntityResolver Integration: Added get_supporting_publications(query, limit) and get_publication_details(identifier) with automated rate limiting and cache support.
• FastMCP Tools: Exposed get_supporting_publications and get_publication_details tools on the MCP server.
• CLI Commands: Added biocontext literature <query> and biocontext paper <identifier> CLI subcommands with tabular rich console formatting.
• Testing: Added comprehensive test suite in tests/test_literature_adapter.py covering PMID, PMCID, DOI lookups, entity searches, and MCP server endpoints.
• Documentation: Updated README.md and docs/API.md reflecting the 12 MCP tools and new CLI subcommands. Bumped version to 0.7.0 in pyproject.toml.