feat(tvix/glue): handle passAsFile

This extends derivation_to_build_request to handle passAsFile the same
way Nix does, and adds a unit test for it.

I opted to making this function fallible (if passAsFile contains a
non-existent env var), rather than pushing all of this into the
Derivation validate function.

Change-Id: I75b635f1f6c0c78d72b9a8fc7824f77e97b69951
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10522
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

tvix/Cargo.lock

@@ -667,9 +667,9 @@ checksum = "56254986775e3233ffa9c4d7d3faaf6d36a2c09d30b20687e9f88bc8bafc16c8"
 
 [[package]]
 name = "digest"
-version = "0.10.6"
+version = "0.10.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8168378f4e5023e7218c89c891c0fd8ecdb5e5e4f18cb78f38cf245dd021e76f"
+checksum = "9ed9a281f7bc9b7576e61468ba615a66a5c8cfdff42420a70aa82701a3b1e292"
 dependencies = [
  "block-buffer",
  "crypto-common",
@@ -2565,9 +2565,9 @@ dependencies = [
 
 [[package]]
 name = "sha2"
-version = "0.10.6"
+version = "0.10.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "82e6b795fe2e3b1e845bafcb27aa35405c4d47cdfc92af5fc8d3002f76cebdc0"
+checksum = "793db75ad2bcafc3ffa7c68b215fee268f537982cd901d132f89c6343f3a3dc8"
 dependencies = [
  "cfg-if",
  "cpufeatures",
@@ -3408,6 +3408,7 @@ dependencies = [
  "data-encoding",
  "lazy_static",
  "nix-compat",
+ "sha2",
  "tempfile",
  "test-case",
  "thiserror",