Pin Cython dependency to <3

[miri64]

DTLSSocket currently does not build with Cython 3.0.0 (released yesterday).

[chrysn]

Note that merely downgrading the language level (as would be achieved by

--- a/DTLSSocket/dtls.pyx
+++ b/DTLSSocket/dtls.pyx
@@ -1,3 +1,4 @@
+# cython: language_level=2

, and is a common fix) is insufficient: Then, the error produced would be

Error compiling Cython file:                                                                                             
------------------------------------------------------------                                                             
...                                                                                                                      
    tdtls.dtls_init()                                                                                                    
    self.ctx = tdtls.dtls_new_context(<void*>self)                                                                       
    self.cb.write = _write                                                                                               
    self.cb.read  = _read                                                                                                
    self.cb.event = _event
    self.cb.get_psk_info = _get_psk_info
                           ^
------------------------------------------------------------ 

DTLSSocket/dtls.pyx:197:27: Cannot assign type 'int (dtls_context_t *, const session_t *, dtls_credentials_type_t, const unsigned char *, size_t, unsigned char *, size_t) except? -1' to 'int (*)(dtls_context_t *, const session_t *, dtls_credentials_type_t, const unsigned char *, size_t, unsigned char *, size_t) noexcept'

and many similar ones.

Pinning this dependency and publishing a new release would be relatively urgent, as it can't easily be installed otherwise.

For a proper fix (with more time), I'd assume that going for language_version=2 first (fixing the function type errors) and then 2to3'ing would be the way to go.

[kabel42]

easy enough, let's go with this now

[miri64]

Thanks!