[BUG] Unsafe calculations in converting interest rates to whole numbers

[purplesmoke05]

Describe the bug

ibet-Prime/app/model/blockchain/token.py

Lines 397 to 398 in fa04154

	if data.interest_rate is not None:
	_interest_rate = int(data.interest_rate * 10000)

Rounding errors would be occur at this point.
(When multiplying by 10000 in Python, this is not a problem because the error is upward. Currently, this does not cause any bugs.)

この箇所で丸め誤差が生じる可能性がある。
（Python上で10000で掛け算を行う場合、誤差が上方向になるため、特に問題にならず、現状もバグが起こることはない。）

Reproduction code

from decimal import Decimal
for i in range(1000000):
    input=Decimal(i)*Decimal(0.0001)
    output=float(input)*10000
    if i != int(output):
            print("This isn't shown")

Expected behavior

Use decimal in multiply.