Upgrade xsync dependency to v4 and update Map API usage

[chimanjain]

Upgrade the github.com/puzpuzpuz/xsync dependency from v3 to v4 and updates all concurrent map usages across the codebase to the updated v4 generic APIs.

In xsync v4, the library has removed the older non-generic structures and consolidated the generic map under xsync.Map.

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Note

Low Risk
Mechanical dependency and type renames on concurrent maps; behavior should match v3 for the same Load/Store/Range usage, with low change surface beyond the library bump.

Overview
Bumps github.com/puzpuzpuz/xsync from v3.5.1 to v4.5.0 and aligns call sites with the v4 generic map API: xsync.MapOf / NewMapOf become xsync.Map / NewMap.

That rename is applied everywhere concurrent maps back proxy networking state: connection tracking (pkg/conntrack), IP allocation (pkg/ippool), Kubernetes port-forward dialer caching (pkg/k8s/k8spf), and tunnel multiplexed connections (pkg/tunnel). go.sum is updated accordingly. The only non-mechanical change is minor slog.Debug formatting in conntrack cleanup.

^{Reviewed by Cursor Bugbot for commit 0358bc8. Bugbot is set up for automated code reviews on this repo. Configure here.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	golang/​github.com/​puzpuzpuz/​xsync/​v4@​v4.5.0

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[chimanjain]

Can the reviewers please verify these changes!