Allow ve = 0 in simBinomialSeasonalExact() for superiority null scenarios

[Copilot]

• Relax ve validation: remove lower bound, allow any finite ve < 1
• Update error message to "ve must be a numeric vector with finite values less than 1"
• Add feasibility check: control_event_rate * (1 - ve) must be in [0, 1)
• Update tests to match new validation rules (error message pattern, ve < 0 positive cases, feasibility error test)
• Update @param ve roxygen doc to document the new valid range
• Bump version number to 3.9.0.9006 in DESCRIPTION
• Update NEWS.md with entry referencing simBinomialSeasonalExact() should allow ve < 0 for no difference (ve = 0) or even experimental worse than control (ve < 0) #267