SPECS: Aggregate Moby sys modules

[cl2t]

Summary

• package the six independently tagged github.com/moby/sys modules from one source spec
• remove the existing standalone atomicwriter and sequential source packages
• preserve each module's real upstream version through its go(...) Provides

The standalone packages and the aggregate package otherwise provide the same capabilities:

go(github.com/moby/sys/atomicwriter)
go(github.com/moby/sys/sequential)

Keeping both layouts produces an OBS/pbuild have choice condition. This migration makes the aggregate package the only provider while following the repository-level packaging approach requested for Moby's multi-module repository.

Validation

• all six official tag archives and RemoteAsset hashes verified
• aggregate source package built successfully on x86_64 and riscv64 in the pure-main OBS project
• pre-commit checks passed
• one source package per signed commit

This is split out of #792 so the provider migration can be reviewed and merged independently. #792 will consume the resulting package rather than carrying the migration itself.

Checklist

• I have read the openRuyi Code of Conduct and agree to abide by it.
• I have read the AI-Assisted Contribution Policy, and this Pull Request includes non-trivial AI-assisted content.

Assisted-by: Claude Code:GPT-5.6 Sol High