Fix dspy task 8635: change min_instr_chars default from 30 to 0

[AlienKevin]

Summary

• The combined.patch for dspy task 8635 adds instruction length bounds to GenerateModuleInstruction and GroundedProposer with min_instr_chars=30
• The pre-existing test test_propose_instructions_for_program[None] uses DummyLM({"proposed_instruction": "instruction"}) which returns "instruction" (11 chars)
• This falls below the 30-char minimum, causing the code to fall back to the default signature instruction ("Given the fields 'question', produce the fields 'answer'.")
• The assertion pred_instructions == ["instruction"] then fails
• tests2.patch already corrects this assertion, but tests1.patch does not — so feature 1 tests always fail when run against the combined implementation

Fix

Change min_instr_chars default from 30 to 0 in both GenerateModuleInstruction.__init__ and GroundedProposer.__init__ within combined.patch. The length-bounds feature remains fully functional when explicitly configured, but the default no longer silently rejects short mock/test instructions.

Test plan

• Oracle test passes for dspy task 8635 (both features)
• Verified on Modal with Harbor evaluation framework