chore: remove passethub

[al3mart]

Summary

• Removes PassetHub support: struct, registry entry, chain spec artifact, and temporary workaround in network spawning
• Replaces passet-hub-spec.json test fixture with coretime-paseo-local.json from paseo-network/runtimes v2.0.6 The smallest fixture from the Paseo chains.
• Restores a previously commented-out assertion in up/mod.rs tests

PassetHub was a temporary chain added for a hackathon. It is no longer needed.

Test plan

• cargo check --locked — compiles
• cargo nextest run --lib --bins -p pop-chains — 222 tests pass

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.87%. Comparing base (79140aa) to head (5adef52).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/pop-chains/src/build/mod.rs	0.00%	0 Missing and 2 partials ⚠️
crates/pop-chains/src/up/mod.rs	50.00%	1 Missing ⚠️

@@            Coverage Diff             @@
##             main    #1005      +/-   ##
==========================================
- Coverage   58.63%   57.87%   -0.77%     
==========================================
  Files         177      176       -1     
  Lines       43679    43654      -25     
  Branches    43679    43654      -25     
==========================================
- Hits        25613    25266     -347     
- Misses      15660    16073     +413     
+ Partials     2406     2315      -91     

Files with missing lines	Coverage Δ
crates/pop-chains/src/registry/mod.rs	93.18% <ø> (+13.40%)	⬆️
crates/pop-chains/src/registry/system.rs	90.82% <ø> (+4.04%)	⬆️
crates/pop-chains/src/up/mod.rs	68.96% <50.00%> (-5.85%)	⬇️
crates/pop-chains/src/build/mod.rs	65.50% <0.00%> (-5.17%)	⬇️

... and 44 files with indirect coverage changes

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[moliholy]

Mostly clean, just one thing: there's a leftover "Passet Hub" reference in crates/pop-cli/src/commands/new/frontend.rs:144. Since PassetHub is being removed, this should probably be updated or removed too, otherwise the Typink template generation would reference a network that no longer exists.