[3.12] gh-121285: Remove backtracking when parsing tarfile headers (GH-121286) (GH-123543)

gh-121285: Remove backtracking when parsing tarfile headers (GH-121286)

* Remove backtracking when parsing tarfile headers
* Rewrite PAX header parsing to be stricter
* Optimize parsing of GNU extended sparse headers v0.0

(cherry picked from commit 34ddb64d088dd7ccc321f6103d23153256caa5d4)

Co-authored-by: Seth Michael Larson <seth@python.org>
Co-authored-by: Kirill Podoprigora <kirill.bast9@mail.ru>
Co-authored-by: Gregory P. Smith <greg@krypto.org>