Fix: adjust tax precise amount when issuing credit notes

[annvelents]

Context

We have this issue that when we issue Invoice, we apply tax on sum of items,
but when we issue a credit note, we apply tax on each item separately.
as result, some values can be rounded in deffirent direction which result in not matching sum.

Example that our client had (all values are amount_cents):

Invoice 001
charge01 = 68_33
charge 02 = 68_33
charge03 = 57_50
charge04 = 85_00

if we apply 20% taxes on the sum of charges, we get:

(68_33 + 68_33 + 57_50 + 85_00) * 1.2 = 334_99,2

but because it is in cents, when issuing the invoice, the value is rounded to 334_99

Next, when we create credit notes for this invoice, and we create a separate CN per each item:

CN01 = 68_33 * 1.2 = 8199.6 => 82_00
CN02 = 57_50 * 1.2 = 69_00
CN03 = 85_00 * 1.2 = 102_00
CN04 = 68_33 * 1.2 = 8199.6 = 82_00

Sum of these credit notes is 335_00 which is more than the invoice total, and we fail vthe validation, despite the fees amount is correct

Description

To help this situation, we can operate adjustments that were made when credit notes are issued.
So when we're creating CN1-3, we simply create credit notes.
when we create CN4, we are subtracting all rounding adjustments that were made for all credit notes for this invoice. in our case, we will need to subtract 0.4 cents from precise taxes amount, and then for the last credit note
CN04 = 68_33 * 1.2 = 8199.6 -0.4 = 8199.2 => 8199
and the values are matching

also removed validation on credit_note_item total amount, as it tries to predict taxes, but they are adjusted further in the credit note creation service

[ancorcruz]

LGTM!