chore: bump version to 0.2.1 with changelog and test coverage

fix: correct MCP protocol version and fix ResourceRegistry memory leak

chore: bump version to 0.2.0

docs: add MIGRATION.md and CHANGELOG.md

fix(examples): update 5 example files for Zig 0.15.x I/O API

docs: update code examples for Zig 0.15.x std.Io API

test(progress): add 6 Writer API tests for ProgressTracker

test(streaming): add 14 edge case tests, fix double-free bug

test(transport): add 8 tests for Transport, StdioTransport, IoSource

test(mcp): add 23 tests for MCPServer, Session, CancellationToken

test(network): add comprehensive tests for Connection and Network structs

fix(streaming): use GenericReader API (readByte/readNoEof) for Zig 0.15.x compatibility

fix(streaming): use readSliceShort/readSliceAll for Zig 0.15.x std.Io.Reader compatibility

fix: complete Zig 0.15.x I/O API compatibility

fix: Zig 0.15.x compatibility - update I/O and ArrayList APIs