Refactor C2 Handlers to use Composition

[google-labs-jules]

This PR refactors the Tavern C2 internal API handlers to adhere to DRY principles using composition.

Changes:

• Created tavern/internal/c2/validation for request validation.
• Created tavern/internal/c2/services/registration for host/beacon lifecycle.
• Created tavern/internal/c2/services/context for entity context loading.
• Created tavern/internal/c2/services/transaction for safe transaction execution.
• Updated ClaimTasks, ReportProcessList, and ReverseShell to utilize these components.

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PR created automatically by Jules for task 14867414180317172930 started by @KCarretto

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[github-actions]

Summary

Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
1577    ±0	1577    ±0	0    ±0	0    ±0	0    ±0	0    ±0	1ms    ±0

Previous Results

Build 🏗️	Result 🧪	Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
#143	✅	1577	1577	0	0	0	0	not captured

Insights

Average Tests per Run	Total Flaky Tests	Total Failed	Slowest Test (p95)
1577	0	0	35.5s

Slowest Tests

Test 📝	Results 📊	Duration (avg) ⏱️	Duration (p95) ⏱️
eldritch: random::string_impl::tests::test_string_uniform	2	34.4s	35.5s
eldritch: random::string_impl::tests::test_string_uniform	2	34.4s	35.5s
eldritch: random::string_impl::tests::test_string_length	2	5.3s	5.5s
eldritch: random::string_impl::tests::test_string_length	2	5.3s	5.5s
eldritch-stdlib-tests: tests::test_all_tomes	2	5.1s	5.2s
eldritch-stdlib-tests: tests::test_all_tomes	2	5.1s	5.2s
eldritch: time::sleep_impl::tests::test_sleep	2	5.1s	5.1s
eldritch: time::sleep_impl::tests::test_sleep	2	5.1s	5.1s
eldritch: pivot::arp_scan_impl::tests::test_lock_failure	2	3.1s	3.2s
eldritch: pivot::arp_scan_impl::tests::test_lock_failure	2	3.1s	3.2s

_{🎉 No failed tests in this run. | 🍂 No flaky tests in this run.}

Github Test Reporter by CTRF 💚