Traffic Router DNS zone calculation optimizations

[srijeet0406]

This PR is not related to any issue. It optimizes the way Traffic Router (TR) calculates the zone(delivery service) of an incoming reuest.

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Which Traffic Control components are affected by this PR?

• Traffic Router

What is the best way to verify this PR?

Make sure all the tests pass.
Run TR locally and make DNS/ HTTP requests against it. If the request is of the form routing name.DS FQDN, the resultant delivery service should be returned from the new map that was introduced in this PR.

If this is a bugfix, which Traffic Control versions contained the bug?

• master

PR submission checklist

• This PR has tests
• This PR has documentation
• This PR has a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[codecov]

Codecov Report

Merging #7641 (c2e9624) into master (7d5cebe) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #7641   +/-   ##
=========================================
  Coverage     30.13%   30.13%           
  Complexity       98       98           
=========================================
  Files           794      794           
  Lines         84060    84060           
  Branches        907      907           
=========================================
  Hits          25333    25333           
  Misses        56597    56597           
  Partials       2130     2130           

Flag	Coverage Δ
traffic_router_unit	29.03% <ø> (ø)

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[zrhoffman]

(this is a re-PR of #7622 with improved performance)