diagnostics_channel: grow native channel storage

[Qard]

Every string-named diagnostics channel currently consumes an entry in a fixed
native subscriber array, so creating more than 1,024 channels terminates the
process at a native CHECK.

Only channels used by native publishers now receive native slots, and the
subscriber buffer grows when it fills. This removes the arbitrary crash while
preserving subscriber tracking and snapshot behavior.

cc @nodejs/diagnostics

[nodejs-github-bot]

Review requested:

• @nodejs/security-wg

[codecov]

Codecov Report

❌ Patch coverage is 85.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.24%. Comparing base (7a11a9b) to head (3a6cf52).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/diagnostics_channel.js	53.84%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #64497   +/-   ##
=======================================
  Coverage   90.24%   90.24%           
=======================================
  Files         739      739           
  Lines      241669   241682   +13     
  Branches    45543    45554   +11     
=======================================
+ Hits       218087   218113   +26     
+ Misses      15150    15112   -38     
- Partials     8432     8457   +25     

Files with missing lines	Coverage Δ
lib/internal/process/pre_execution.js	98.07% <100.00%> (+0.13%)	⬆️
src/node_diagnostics_channel.cc	83.51% <100.00%> (+1.64%)	⬆️
src/node_diagnostics_channel.h	57.14% <ø> (ø)
lib/diagnostics_channel.js	97.57% <53.84%> (-0.59%)	⬇️

... and 38 files with indirect coverage changes

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