perf: Auto Attendance processing

[ruchamahabal]

Auto attendance job times out with scale.

Before:

After:

Tested with data: 1000 employees, 10,000 check-ins

Optimizations:

• Added simple indexing on widely queried columns to avoid full table scans: Shift Type and Employee in Employee Checkin
• get_doc -> db_exists or get_value
• db.get_all -> db.exists or get_value
• Caching: get_cached_doc / get_cached_value / get_value with db_cache (as per use case_

[codecov-commenter]

Codecov Report

Merging #517 (2971dc1) into develop (7579a94) will increase coverage by 0.01%.
The diff coverage is 66.66%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #517      +/-   ##
===========================================
+ Coverage    73.03%   73.04%   +0.01%     
===========================================
  Files          190      190              
  Lines         9842     9839       -3     
===========================================
- Hits          7188     7187       -1     
+ Misses        2654     2652       -2     

Impacted Files	Coverage Δ
hrms/hr/doctype/shift_type/shift_type.py	90.90% <33.33%> (ø)
...ms/hr/doctype/employee_checkin/employee_checkin.py	93.54% <100.00%> (ø)
...ms/hr/doctype/shift_assignment/shift_assignment.py	91.37% <100.00%> (ø)

... and 2 files with indirect coverage changes