feat: raw bin IO support

[Mr-Ao-Dragon]

目前如果需要直传bin还需要手动转换，很不方便，希望能添加直接输入输出bin的功能。

[idlesign]

And where exactly do you want to pass binary? Could you provide an example?

[Mr-Ao-Dragon]

@idlesign Concrete changes in FurryChatWorld#1:

Input side — isinstance autotype, str path unchanged:

• SRPSessionBase.__init__(private=) — accepts int / bytes / hex str
• SRPServerSession.__init__(password_verifier=) — same
• init_base(salt) — bytes passthrough, str still unhexlify
• init_common_secret(other_public) — int / bytes / hex str
• process(other_public, salt, base64=False) — signature unchanged;
  adds bytes+base64 mutual-exclusion check; bytes bypasses
  _value_decode and flows to the autotype init_* directly
• verify_proof(key_proof, base64=False) — bytes branch compares
  against internal _key_proof / _key_proof_hash (bytes) instead of
  the hex-str properties
• get_user_data_triplet(base64=False, binary=False) — new
  binary=True emits bytes (verifier prime-width, salt bits_salt-width)

Incidental fix: utils.hex_from() returned bytes on Py3 via
hexlify, str on Py2. All call sites assumed str. My
isinstance(salt, bytes) branch in init_base turned this latent
inconsistency into a real bug. Fixed with .decode('ascii').

The one consistency-breaking change:

init_common_secret now raises SRPException instead of ValueError
when given a non-hex str. Previously int_from_hex(non_hex) leaked
ValueError from int(s, 16). This is a private method, and the new
behavior aligns with the rest of the library (everything else raises
SRPException), but code catching ValueError explicitly would break.

9 new tests in tests/test_binary.py, all 15 pass. Existing hex/base64
paths unchanged.

[Mr-Ao-Dragon]

this a my test result

[Mr-Ao-Dragon]

Status: This is running in our internal fork right now. We'll put it
through our production SRP flows over the next release cycle to confirm
there are no edge cases the test suite misses. Once it's battle-tested
on our side, I'll open a PR here — no pressure to review until then,
but feedback on the direction is welcome anytime.

[idlesign]

Thank you.

Last year I've been thinking on dropping Python 2 support entirely and siwtch to packaging tools for this project. I'll try to do so this week. Thus your PR would probably need to be rebased.

By the way do you use Python 2?

[Mr-Ao-Dragon]

Thank you.

Last year I've been thinking on dropping Python 2 support entirely and siwtch to packaging tools for this project. I'll try to do so this week. Thus your PR would probably need to be rebased.

By the way do you use Python 2?

is python 3, but I intentionally used Python 2 syntax. By the way, if you're considering an upgrade, you might as well consider switching directly to uv.

No objections to rebase; I'm also happy to switch to a more modern packaging tool.

[idlesign]

you might as well consider switching directly to uv.

yeap

[idlesign]

I've updated the repository at last.
It seems that your pull request needs to be updated. Sorry for inconvenience.

[Mr-Ao-Dragon]

I've updated the repository at last. It seems that your pull request needs to be updated. Sorry for inconvenience.

It's okay. I'll handle it.

[Mr-Ao-Dragon]

#12 upstream change now marged

[Mr-Ao-Dragon]

@idlesign