refactor: remove the default timeout for executables

[jahvon]

Removed the default value (30m0s) for the Timeout field in flowfile_schema.json and flowfile.md. This aligns with the new approach of treating Timeout as optional.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 21.91%. Comparing base (b944b8c) to head (946a89e).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
types/executable/executable.go	25.00%	2 Missing and 1 partial ⚠️
internal/cache/executable_generator.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #239      +/-   ##
==========================================
- Coverage   22.07%   21.91%   -0.16%     
==========================================
  Files          84       84              
  Lines        6958     7026      +68     
==========================================
+ Hits         1536     1540       +4     
- Misses       5145     5208      +63     
- Partials      277      278       +1     

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