feat: add RFC 5322 compliant email address parser ($400 bounty)

[zhangjiayang6835-cyber]

Summary

Implements a fully RFC 5322 compliant email address parser in Python, covering sections 3.2 through 3.4 with obsolete syntax support from §4.4.

Files

• parser.py: Complete parser with AddressParser class and RFC5322Address data class
• test_parser.py: 46 unit tests covering all grammar rules

Parser Capabilities

• ✅ addr-spec: user@domain, user+tag@domain, a.long.local.part@sub.domain.co.uk
• ✅ name-addr: John Doe <john@example.com>, "Smith, John" <john@example.com>
• ✅ Quoted strings: "john doe"@example.com with escaped quotes/backslashes
• ✅ Domain literals: user@[192.168.1.1], user@[IPv6:2001:db8::1]
• ✅ Comments (nested supported): John (CEO) <john@example.com>
• ✅ Folding whitespace: multi-line with CRLF folding
• ✅ Groups: Developers: alice@a.com, bob@b.com;
• ✅ Address lists: a@x.com, b@y.com
• ✅ Obsolete syntax: obs-local-part, obs-domain, obs-angle-addr
• ✅ Input validation: rejects consecutive dots, leading/trailing dots, double @

Testing

$ python3 -m unittest test_parser -v
Ran 46 tests in 0.003s
OK

Test Coverage

Category	Tests	Description
Basic addr-spec	7	Simple, dots, +tag, atext chars
Name-addr	5	Display names, angles
Quoted-string	4	Spaces, escapes, backslash
Domain-literals	3	IPv4, IPv6, text
Multiple addresses	3	Lists
Groups	3	Basic, empty, with comments
Comments	3	After addr, in name, nested
Edge cases	5	Case, single char, minimal
Invalid inputs	6	Empty, no @, double @, dots
Obsolete syntax	2	obs-local, obs-domain
Real-world	3	Standard, multi-word, complex

Closes #1