Remove tldextract from core dependencies to drop the requests stack

[vdusek]

Problem

tldextract is a core dependency used in one place — _utils/urls.py (_domain_under_public_suffix()), only for the opt-in same-domain enqueue strategy. The default strategy everywhere is same-hostname, so for most users it never runs. Two issues:

1. It's the only reason the requests stack is in every install. Nothing in src/crawlee imports requests directly. Removing tldextract drops 7 packages / ~1.8 MB:

   tldextract, requests, requests-file, filelock, urllib3, certifi, charset-normalizer
   (idna stays — needed by yarl)
   

2. It hits the network on first use. TLDExtract(cache_dir=tempfile.mkdtemp()) + tldextract defaults → the first same-domain lookup tries to fetch the PSL over the network before falling back to the bundled snapshot (and writes a disk cache, which breaks on read-only filesystems).

What we actually need

Given a host, get its registrable domain (eTLD+1) from the Public Suffix List. For same-domain we only compare two hosts for equality.

Options (with runtime dep counts)

#	Approach	New deps	Effect
A	Vendor a PSL snapshot + ~40-line matcher (like Crawlee JS / tldts)	0	removes all 7 pkgs, no network; we refresh snapshot via CI
B1	Swap for publicsuffixlist	1 (0 transitive)	net −6 pkgs; pure Python, bundles PSL, auto-updated daily, actively maintained
B2	Swap for tld	1 (0 transitive)	net −6 pkgs; pure Python, bundles PSL, slower cadence
B3	Swap for publicsuffix2	1 (0 transitive)	net −6 pkgs; unmaintained since 2019 — avoid
C	Lazy-import + move tldextract to an extra	0 default / 7 for same-domain	keeps network fetch, only hides the problem
D	Naive "last two labels", no PSL	0	removes all 7 pkgs but breaks .co.uk, github.io, … — not acceptable

Recommendation: A (vendored snapshot) — zero deps, no network, full control. If we'd rather not maintain a snapshot, B1 (publicsuffixlist) is the best fallback.

same-domain behavior must stay correct for multi-part suffixes; add test cases in tests/unit/_utils/test_urls.py.

[vdusek]

I believe we should try to do option A, with a regular CI refresh.