net/textproto: excessive CPU consumption in Reader.ReadResponse (CVE-2025-61724) [1.24 backport]

[gopherbot]

@neild requested issue #75716 to be considered for backport to the next 1.24 minor release.

@gopherbot please open backport issues for this security fix

[gopherbot]

Change https://go.dev/cl/709837 mentions this issue: [release-branch.go1.24] net/textproto: avoid quadratic complexity in Reader.ReadResponse

[gopherbot]

Closed by merging CL 709837 (commit a402f4a) to release-branch.go1.24.