fix(fleetcontrol): paginate fleet search across all pages

[ShaneLillieNR]

fleetcontrol fleet search --name-equals/--name-contains only inspected the first page of GetEntitySearch results, so the client-side name filter silently missed any fleet that wasn't on page 1 (confirmed live: a known fleet absent from a 100-entity first page, found instantly via a name-scoped query against the general entitySearch API).

searchFleetEntities now loops on NextCursor (capped at 1000 pages as a safety net against a misbehaving cursor) and accumulates entities across every page before applying the name filter. This intentionally does not expose a --next-cursor flag the way fleet members list does - a name search's entire point is "does this exist," and the caller has no way to know which page a match might be on, so partial/manual paging would defeat the feature.

Depended on newrelic/newrelic-client-go#1442, which fixed the same bug one layer down: GetEntitySearch's cursor parameter was a no-op because the generated query never declared/passed $cursor. That PR has merged and shipped in client-go v2.93.2 - go.mod now points at the real release instead of the temporary commit-pinned replace directive, so this is ready for review.

Test plan

• internal/fleetcontrol/fleet_management_search_test.go: 5 unit tests against a mock NerdGraph server - match on page 1, match only on page 2+ (the regression test for this bug), no match across all pages, error on a later page propagates (no partial results), --name-contains spanning multiple pages.
• Verified the page-2 regression test isn't vacuous: temporarily capped the loop at one iteration and confirmed that test fails, then restored the fix.
• make test-unit - 526 tests passing. gofmt / golangci-lint clean.
• Live-verified against a real account (~800 fleets) with the actual built binary: unfiltered search returns all 798 fleets with no duplication, and --name-equals finds fleets at page 2+ that a pre-fix build returns null for. Details in the PR comments.

[ShaneLillieNR]

Live end-to-end verification of this fix, using the built newrelic-cli binary against a real account (~800 fleets), not just the unit tests in this PR:

With this fix (built against newrelic/newrelic-client-go#1442's commit via the temporary go.mod replace directive):

• Unfiltered fleetcontrol fleet search returns 798 fleets, all 798 IDs unique — confirms the pagination loop walks every page (~8 pages at 100/page) with no overlap or duplication.
• --name-equals correctly finds fleets that only exist beyond page 1 — tested one at result index 150 and the very last one at index 797.

Without this fix (same live account, same two fleet names, built from main with unpatched newrelic-client-go v2.91.0 in a throwaway worktree): both --name-equals queries returned null. That's the exact bug being fixed — silently wrong empty results for any fleet not on page 1, no error, no warning.

[pranav-new-relic]

LGTM (as discussed over the call). Thanks for fixing this :)