time: add MMM pattern support for parse_format()

[jeffangelion]

Add three-letter month names parsing via time.parse_format()
Test code:

import time
a := time.now()
println(a)
b := a.custom_format('MMM DD HH:mm:ss YYYY')
println(b)
println(time.parse_format(b, 'MMM DD HH:mm:ss YYYY')!)

🤖 Generated by Copilot at 2ca6223

Add support for parsing month names in different languages in time module. Use MMM format specifier and a new method to handle month abbreviations in date_time_parser.v.

🤖 Generated by Copilot at 2ca6223

• Add support for parsing month names in different languages using the MMM format specifier (link)

• Call must_be_valid_three_letter_month method to parse and validate the month abbreviation from the input string (link)
• Assign the returned month number to the month_ variable (link)

• Implement must_be_valid_three_letter_month method for DateTimeParser struct (link)
  • Check that the input string has at least three characters (link)
  • Convert the first three characters to uppercase and compare them with a map of valid month abbreviations (link)
  • Return the corresponding month number or an error if the abbreviation is invalid (link)

[jeffangelion]

Now it can be tested via time_test.v