Migrate filter DSL to the filt-rs crate

[Copilot]

Replaces the in-tree src/filter module with the extracted filt-rs crate. This is a near drop-in swap that also brings glob (like) and regex (matches) pattern matching, plus native datetime filtering.

Changes

• Dependency: add filt-rs 1.1.0 with the chrono, regex, and serde features; re-export Filter/FilterValue/Filterable from filt_rs in main.rs.
• Remove the entire src/filter/ module (lexer, parser, interpreter, value, etc.).
• Lifetime parameter: FilterValue → FilterValue<'_>. Metadata caches FilterValue<'static> (entries outlive the entity they derive from) and insert now accepts any Into<FilterValue<'a>>, so call sites keep passing &str rather than allocating Strings.
• Native timestamps: expose chrono datetimes as filter fields — repo.pushed_at/created_at/updated_at, release.created_at/published_at, asset.created_at/updated_at, and gist.created_at/updated_at (gist fields changed from String to DateTime<Utc>).
• Docs: document like/matches, the _cs case-sensitive variants, raw strings, duration literals and now()/trim(); add the new datetime fields to the repo/release/gist reference tables; correct the equality note to reflect Unicode case-folding.

New filtering capabilities

repo.name like "*-backup"                       # glob match (resolves #36's request)
repo.name matches r"^release/v\d+(\.\d+){2}$"   # regular expression match
repo.pushed_at > now() - 30d                    # native datetime comparison

[notheotherben]

@copilot let's use repo.name like "*-rs" as an example instead; since the example provided here implies that repo names can include slashes (which is not the case).

[Copilot]

Updated the example to repo.name like "*-rs" in 2086f63.

[Copilot]

Correction: the change is in commit 4b10b94.

[notheotherben]

@copilot Let's also update the field and example used here to be more realistic (for example, checking that the release.tag matches a semver version number).

[notheotherben]

@copilot Let's also update the field and example used here to be more realistic (for example, checking that the release.tag matches a semver version number).

[Copilot]

Updated the example to release.tag matches r"^v\d+(\.\d+){2}$", matching semver tags like v1.2.3, in 3e76e6f.

[codecov]

Codecov Report

❌ Patch coverage is 96.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 70.87%. Comparing base (f385e2a) to head (3e76e6f).

Files with missing lines	Patch %	Lines
src/entities/mod.rs	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #590      +/-   ##
==========================================
- Coverage   72.64%   70.87%   -1.77%     
==========================================
  Files          36       28       -8     
  Lines        2709     1971     -738     
==========================================
- Hits         1968     1397     -571     
+ Misses        741      574     -167     

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