Introduce the basic skeleton for the compiler (#74)

* Implement the skeleton of a pass infrastructure

While it is incomplete, an initial skeleton for the pass management
infrastructure ensures that we do not paint ourselves into any corners
that might be hard to design our way out of later. It provides the
infrastructure for creating and managing passes, as well as shuffling
pass data between passes.

Please note that this we make use of self-referential structs via
Ouroboros to better encapsulate the LLVM context and the modules that
exist in it.

Added `libffi` and `libxml2` as build and runtime dependencies to the
project as these are required by inkwell now that it is actually in use.
This fixes an issue preventing compilation in tests.

* Implement the module mapping pass

This pass runs an analysis of LLVM modules to resolve all top-level
entities. The results are written out as pass data, and are intended for
use as part of a consistency check during the compilation to FLO.

As part of implementing this pass, this commit also implements:

- A proxy for the portions of the LLVM type system that we support,
  enabling us to do pre- and during-compilation consistency checking
  where necessary.
- A parser for LLVM's data-layout specifications, allowing us to ensure
  that the provided modules are not making any assumptions that would be
  unsafe for our target machine.

* Miscellaneous fixes and updates

This commit performs a number of small miscellaneous refactorings and
fixes in response to looking at the code with a fresh set of eyes. It
also accounts for feedback given during code review.

Cargo.toml

@@ -32,8 +32,10 @@ anyhow = "1.0.89"
 ariadne = "0.4.1"
 bimap = { version = "0.6.3", features = ["serde"] }
 clap = "4.5.16"
+inkwell = { version = "0.5.0", features = ["llvm18-0"] }
 itertools = "0.13.0"
 ltc-cli = { path = "crates/cli" }
+ltc-compiler = { path = "crates/compiler" }
 ltc-driver = { path = "crates/driver" }
 ltc-errors = { path = "crates/error" }
 ltc-flo = { path = "crates/flo" }

crates/cli/Cargo.toml

@@ -17,6 +17,7 @@ rust-version.workspace = true
 ariadne.workspace = true
 clap.workspace = true
 itertools.workspace = true
+ltc-compiler.workspace = true
 tracing.workspace = true
 
 [[bin]]