Avoid deep copy in entity lookup

[krdln]

We never mutate entities directly in the maps, so copying was not necessary.
Also, added added a type wrapper so it's less likely someone tries mutating the
returned entity.

Drive-by:

• Stop using proto-generated structs for Entities datastructure.
• Fix lock in Clear() (fortunately, used only in tests).

Ref: #2170

Checklist

• Tested in playground or other setup
• Screenshot (Grafana) from playground added to PR for 15+ minute run (forgot to paste 🤦)
• Tests and/or benchmarks are included – already covered by existing tests

Summary by OpenAI

Refactor:

• Replaced proto-generated structs with custom Entities data structure
• Added type wrapper to prevent direct mutation of entities
• Removed unnecessary deep copy in entity lookup
• Fixed lock issue in Clear() function

🎉 No more deep copy, we're swift and light,
Type wrappers guard our entities right.
Locks are fixed, and code's refined,
A better version, now combined. 🚀

[github-actions]

🤖 OpenAI

The changes in this pull request focus on improving performance, maintainability, and modularity by removing unnecessary deep copy in entity lookup, adding a type wrapper to prevent direct mutation of entities, replacing proto-generated structs for Entities data structure, and fixing a lock in the Clear() function.

Files	Summary
pkg/discovery/entities/entities-service.go, pkg/discovery/entities/entities.go, pkg/discovery/entities/entities_test.go, extensions/fluxninja/heartbeats/services_test.go	The changes involve adding a new type wrapper, removing deep copy, and fixing a lock, which can impact the behavior of the code.
pkg/policies/flowcontrol/service-getter/service-getter.go, pkg/policies/flowcontrol/service-getter/service-getter_test.go, pkg/policies/flowcontrol/service/check/check_test.go, pkg/policies/flowcontrol/service/checkhttp/checkhttp_test.go, pkg/policies/flowcontrol/service/envoy/authz_test.go	The changes are minor and do not impact the logic or functionality significantly.
pkg/discovery/entities/entities.go	The changes improve performance, maintainability, and modularity by removing the deep copy of entities in maps, adding a type wrapper to avoid direct mutation, replacing proto-generated structs, and fixing a lock.

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In the recent run, only the files that changed from the base of the PR and between 2ff7dfa89761398ba1c7aad6d25c20e8b7db4e62 and 8ee3b5ffa1c2941f53aec017974501a5b0be34a3 commits were reviewed.

Files not reviewed due to simple changes (7)

Skipped review in the recent run

• extensions/fluxninja/heartbeats/services_test.go
• pkg/discovery/entities/entities.go
• pkg/discovery/entities/entities_test.go
• pkg/policies/flowcontrol/service-getter/service-getter_test.go
• pkg/policies/flowcontrol/service/check/check_test.go
• pkg/policies/flowcontrol/service/checkhttp/checkhttp_test.go
• pkg/policies/flowcontrol/service/envoy/authz_test.go