fix: Get file extension from file path and changes use of reserved word 'format' to 'fmt'

[ciceroadf]

I've run the following test code:

import asyncio
from pydoll.browser.chrome import Chrome
from pydoll.constants import By

async def main():
    # Start the browser with no additional webdriver configuration!
    async with Chrome() as browser:
        await browser.start()
        page = await browser.get_page()
        
        # Navigate through captcha-protected sites without worry
        await page.go_to('https://www.example.com')
        await page.get_screenshot('./ss.png')
        

asyncio.run(main())

It saved ss.png in the root directory, as expected, but when i tried to open it with the ubuntu's default image visualizer, i got the following error:

When i tried to change it to jpeg, it worked just fine, so i've implemented some logic to get the file extension from the file path given by the developer, i've also changed the use of the reserved word "format" to "fmt" to avoid problems.

[ciceroadf]

I've implemented the changes requested

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pydoll/browser/page.py	80.00%	1 Missing :warning:
pydoll/exceptions.py	75.00%	1 Missing :warning:

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Flag	Coverage Δ
tests	97.30% <80.00%> (+1.08%)	:arrow_up:

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Files with missing lines	Coverage Δ
pydoll/commands/page.py	98.18% <100.00%> (ø)
pydoll/element.py	98.41% <ø> (ø)
pydoll/browser/page.py	95.34% <80.00%> (-0.49%)	:arrow_down:
pydoll/exceptions.py	75.00% <75.00%> (ø)

... and 1 file with indirect coverage changes

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