fix(readme): align function signatures, Comparable type, and search sort requirement with actual implementation

[Copilot]

README had several inaccuracies relative to the actual TypeScript definitions and runtime behavior.

Fixes:

• Comparable type: Added missing bigint and object to match src/utils/index.ts; notes now clarify that object requires a custom compareFn since defaultCompare throws for it
• Function signatures: Replaced bare sortFn<T>(...) / searchFn<T>(...) (invalid TS) with declare function syntax
• Search sort requirement: Narrowed overly broad "must pre-sort before Search" note — only binarySearch and jumpSearch require a sorted array; linearSearch and quickSearch work on unsorted input
• Spacing: Fixed Types usedโดย → Types used โดย

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