add the is_numeric method

[useroutofbound]

Add is_numeric() to TJValue

Closes #49

Summary

Adds a virtual is_numeric(bool strict = false) const method to TJValue so any JSON value can report whether it is numeric. In non-strict mode, strings containing a valid number also count as numeric.

Changes

src/TinyJSON.h

• Added virtual bool is_numeric(bool strict = false) const; to TJValue.

src/TinyJSON.cpp

Class	Behavior
TJValue (base)	Returns false
TJValueNumber	Always returns true
TJValueString	Returns false if strict; otherwise scans characters to validate a number (optional sign, decimal point, scientific notation)
TJValueObject, TJValueArray, TJValueBoolean, TJValueNull, TJValueComment	Return false

Behavior

Input	strict = false	strict = true
Number 42	true	true
String "42"	true	false
String "-3.14e2"	true	false
String "abc"	false	false
String ""	false	false
Boolean / null / array / object	false	false

Notes

• Non-breaking: strict defaults to false and the method is purely additive.
• Strict mode only accepts real TJValueNumber instances.

[useroutofbound]

I have fixed the build issues by adding the override specifiers to the
is_numeric declarations in all derived classes within src/TinyJSON.h.

[useroutofbound]

I have fixed the build issues by adding the override specifiers to the
is_numeric declarations in all derived classes within src/TinyJSON.h.

[FFMG]

Thanks for this PR, but you will need to add some tests as well please.

Especially for the TJValueString but for all cases really.

[useroutofbound]

Added new test file and also fixed the unused parameter warning