feat: enhanced error handling in parseAlphaNumTime fn

[gouthamhusky]

Description

Enhanced the error handling in the parseAlphaNumTime() to deal with invalid string inputs that do not adhere to the 'now-[Num][Unit]' format

Fixes #539 : Add error handling to parseAlphaNumTime

Testing

Added 3 more cases to the Test_parseAlphaNumTime() method of the searchHandler_test.go file with the following input strings:

• invalidTimeString: an invalid string that would cause the method to return the default value
• now-365x: an input with an invalid time unit of 'x'
• now-5xm: input with an invalid number '5x', which would cause an integer parsing error

Checklist:

• [✅] I have self-reviewed this PR.
• [✅] I have removed all print-debugging and commented-out code that should not be merged.
• [✅] I have added sufficient comments in my code, particularly in hard-to-understand areas.
• [✅] I have formatted the code, if applicable. For Go, I have run goimports -w ..