Stub out tzdb support to unblock Now and ZonedDateTime (#99)

And thus begins the Great Time Zone / `ZonedDateTime` implementation.
:sweat_smile:

This stubs out `tzdb` support by relying solely on the user's zoneinfo
files, and should allow us to move forward with implementing and testing
`ZonedDateTime` without being blocked by a proper tzdb provider for Boa.

This PR implements:

  - `Now` builtin
  - `FsTzdbProvider` stub
- Some `ZonedDateTime` APIs along with experimental, non-engine focused
APIs.
  
Things of note that are not in this PR:
  
- Handling POSIX's [proleptic tz
format](https://snapshots.sourceware.org/glibc/trunk/2024-06-27_16-55_1719507301/manual/html_node/Proleptic-TZ.html)
and non-fat version of the TZDB.
  - Any thing zoneinfo / `zic` related.
  - Tests for more time zone edge cases
  - Many `ZonedDateTime` methods and abstract ops
  - **Windows Support**
  
Let me know what you think :)

Author: nekevss

Cargo.lock

@@ -9,7 +9,7 @@ edition = "2021"
 authors = ["boa-dev"]
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/boa-dev/temporal"
-rust-version = "1.79"
+rust-version = "1.80"
 exclude = [
     "docs/*",
     ".github/*",
@@ -26,6 +26,11 @@ num-traits = "0.2.19"
 ixdtf = { version = "0.2.0", features = ["duration"]}
 log = { version = "0.4.0", optional = true }
 
+tzif = { version = "0.2.3", optional = true }
+iana-time-zone = "0.1.61"
 
 [features]
 log = ["dep:log"]
+experimental = ["tzdb"]
+tzdb = ["dep:tzif", "std"]
+std = []