feat: complete namespace support (Podcast 2.0, Media RSS, GeoRSS)

[bug-ops]

Summary

This PR completes all missing namespace functionality for feedparser-rs across three phases:

Phase 1: Podcast 2.0 + iTunes ✅

• Add PodcastChapters type for podcast:chapters element
• Add PodcastSoundbite type for podcast:soundbite element
• Add PodcastEntryMeta container for entry-level podcast metadata
• Add itunes:complete and itunes:new-feed-url fields to ItunesFeedMeta
• Add DoS limits: max_podcast_transcripts, max_podcast_funding, max_podcast_persons, max_podcast_soundbites
• Add SSRF security warnings to all URL fields
• Optimize parse_duration() and parse_explicit() to avoid allocations

Phase 2: Media RSS + podcast:value ✅

• Add MediaContent with full Media RSS spec (medium, bitrate, framerate, expression, isDefault)
• Add MediaThumbnail with NTP time offset support
• Add PodcastValue and PodcastValueRecipient for value-for-value monetization
• Implement podcast:value parsing with nested valueRecipient elements
• Add max_value_recipients DoS limit (default: 20)
• Add media_content_to_enclosure() conversion helper

Phase 3: Compat Module + GeoRSS ✅

• Add compat module with Python feedparser compatibility helpers:
  • normalize_version() converts FeedVersion to Python format
  • format_duration() converts seconds to HH:MM:SS
  • is_valid_version() validates version identifiers
• Add geo field to FeedMeta for feed-level geographic data
• Add GeoRSS parsing at channel level in RSS and RSS 1.0 parsers

Breaking Changes

• Entry struct now has podcast: Option<PodcastEntryMeta> field

Quality Assurance

All three phases passed:

• ✅ Performance review (rust-performance-engineer)
• ✅ Security audit (rust-security-maintenance)
• ✅ Testing review (rust-testing-engineer)
• ✅ Code review (rust-code-reviewer)

Test Results

• ✅ 574 tests pass
• ✅ Clippy passes with no warnings
• ✅ Code formatted with cargo +nightly fmt
• ✅ Test coverage >85% for new code

Files Changed

• Types: podcast.rs, feed.rs, entry.rs, common.rs, mod.rs
• Parsers: rss.rs, rss10.rs, common.rs
• Namespaces: media_rss.rs, georss.rs
• New: compat/mod.rs
• Limits: limits.rs (core + py bindings)
• Tests: test_podcast_namespace.rs + inline tests

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.76674% with 28 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/feedparser-rs-core/src/parser/rss10.rs	6.25%	15 Missing ⚠️
crates/feedparser-rs-core/src/parser/rss.rs	95.57%	13 Missing ⚠️

@@            Coverage Diff             @@
##             main      #35      +/-   ##
==========================================
+ Coverage   91.55%   92.14%   +0.59%     
==========================================
  Files          33       34       +1     
  Lines        6616     7446     +830     
==========================================
+ Hits         6057     6861     +804     
- Misses        559      585      +26     

Flag	Coverage Δ
rust-core	92.14% <96.76%> (+0.59%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
crates/feedparser-rs-core/src/compat/mod.rs	100.00% <100.00%> (ø)
crates/feedparser-rs-core/src/lib.rs	20.95% <ø> (ø)
crates/feedparser-rs-core/src/limits.rs	100.00% <100.00%> (ø)
crates/feedparser-rs-core/src/namespace/georss.rs	96.11% <100.00%> (+1.55%)	⬆️
...ates/feedparser-rs-core/src/namespace/media_rss.rs	97.69% <100.00%> (+3.57%)	⬆️
crates/feedparser-rs-core/src/parser/common.rs	77.63% <100.00%> (+0.29%)	⬆️
crates/feedparser-rs-core/src/types/common.rs	86.46% <ø> (ø)
crates/feedparser-rs-core/src/types/entry.rs	87.69% <ø> (ø)
crates/feedparser-rs-core/src/types/feed.rs	96.36% <ø> (ø)
crates/feedparser-rs-core/src/types/podcast.rs	100.00% <100.00%> (ø)
... and 2 more

... and 1 file with indirect coverage changes

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