feat(pilota-build): support codegen for input IDLs without services

[junliurs]

Motivation

Solution

[codecov]

Codecov Report

❌ Patch coverage is 85.91224% with 61 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.20%. Comparing base (f0d1138) to head (f1046d7).

Files with missing lines	Patch %	Lines
pilota-build/src/lib.rs	54.73%	43 Missing ⚠️
pilota-build/src/middle/root_selector.rs	94.23%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #363      +/-   ##
==========================================
+ Coverage   67.89%   68.20%   +0.30%     
==========================================
  Files          88       89       +1     
  Lines       25404    25775     +371     
==========================================
+ Hits        17249    17579     +330     
- Misses       8155     8196      +41     

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