chore: deprecate TestFetcher for now

[Serial-ATA]

It hasn't been used for its intended purpose for awhile now (integration tests with the manager), but it could potentially be useful again in the future.

[claude]

Claude finished @Serial-ATA's task —— View job

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PR Review: Deprecate TestFetcher ✅

Todo List:

• Read CLAUDE.md for repo-specific guidelines (none found)
• Analyze the 4 changed files to understand the deprecation
• Review code quality and deprecation approach
• Check for potential bugs or issues
• Evaluate performance considerations
• Assess security implications for the substrate blockchain
• Verify documentation updates are appropriate
• Provide comprehensive review feedback

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Review Summary

This PR correctly deprecates the TestFetcher struct with proper Rust deprecation attributes. The changes are well-implemented and follow best practices.

✅ Code Quality & Best Practices

The deprecation approach is excellent:

• Proper deprecation attribute: Uses #[deprecated(since = "1.4.4", note = "...")] at primitives/src/services/sources.rs:151-154
• Clear deprecation message: Explains why it's deprecated and potential future use
• Consistent application: Applied in both source code and generated subxt code
• Documentation updated: README.md reflects the deprecation in code generation

✅ No Bugs or Issues Found

• The TestFetcher remains functional while deprecated (no breaking changes)
• All enum variants in BlueprintSource remain intact
• Type safety preserved across the codebase

✅ Performance Considerations

• Zero runtime impact: Deprecation is compile-time only
• No memory overhead: No additional allocations or data structures
• Metadata size: Minor increase in compiled metadata due to deprecation attributes

✅ Security Assessment

No security implications - this is a deprecation-only change:

• Does not modify any security-critical functionality
• No new attack vectors introduced
• Existing validation and constraints remain unchanged
• The TestFetcher was for development/testing only (not production)

✅ Documentation & Consistency

Comprehensive documentation updates:

• README.md: Updated subxt codegen command to include deprecation attribute
• Generated code: Both tangle_testnet_runtime.rs and metadata files updated
• TypeScript types: Will need regeneration to reflect deprecation (external)

🔍 Minor Observations

1. TypeScript types (types/ directory) still reference TestFetcher without deprecation markers - these appear to be auto-generated from metadata
2. Consider cleanup timeline: The deprecation note mentions "may be used in the future" - consider adding a target version for potential removal

Recommendation: ✅ APPROVE

This is a clean, well-executed deprecation that follows Rust and Substrate best practices. The changes are minimal, safe, and properly documented.

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