fix: create inline buildpack for python+pack

[gauron99]

python + pack works now

• Remove pyScaffoldInjector that hijacked Docker tar streams to inject scaffolding
• Enable Python scaffolding via Scaffolder (writes to .func/build/ like Go)
• Use inline pre-buildpack to rearrange workspace at build time (user code → fn/, scaffolding → root)
• Replicate inline buildpack logic in Tekton task for remote builds
• Add more scaffolding tests

/fixes #3405
/fixes #2985
/fixes #3007

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Fixes #

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[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.94%. Comparing base (a42c16f) to head (859038d).
⚠️ Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/buildpacks/scaffolder.go	78.94%	8 Missing and 4 partials ⚠️
pkg/buildpacks/builder.go	65.21%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3425      +/-   ##
==========================================
+ Coverage   54.51%   54.94%   +0.42%     
==========================================
  Files         179      178       -1     
  Lines       20274    20281       +7     
==========================================
+ Hits        11053    11143      +90     
+ Misses       8049     7960      -89     
- Partials     1172     1178       +6     

Flag	Coverage Δ
e2e	38.60% <5.08%> (+0.15%)	⬆️
e2e go	32.79% <5.08%> (+0.15%)	⬆️
e2e node	28.56% <3.38%> (+0.01%)	⬆️
e2e python	33.14% <76.27%> (+0.99%)	⬆️
e2e quarkus	28.71% <3.38%> (+0.01%)	⬆️
e2e rust	28.12% <3.38%> (+0.01%)	⬆️
e2e springboot	26.56% <3.38%> (-0.01%)	⬇️
e2e typescript	28.67% <3.38%> (+0.01%)	⬆️
integration	17.57% <0.00%> (+<0.01%)	⬆️
unit macos-14	42.76% <62.71%> (+0.53%)	⬆️
unit macos-latest	42.76% <62.71%> (+0.53%)	⬆️
unit ubuntu-24.04-arm	43.02% <57.50%> (+0.48%)	⬆️
unit ubuntu-latest	43.65% <62.71%> (+0.52%)	⬆️
unit windows-latest	42.78% <62.71%> (+0.52%)	⬆️

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