Multi-version notebook support

[MichaelHatherly]

This adds support for running notebook processes that are different Julia versions than the main runner process. To start a different Julia version in a notebook use juliaup channel syntax in the julia.exeflags frontmatter for the notebook. You must already have that channel name installed:

---
engine: julia
julia:
    exeflags: ["+1.11"]
---

Previously this did not work since QNR used Malt.jl for managing them, and that package uses Serialization.jl for the communication between processes. Serialization is limited to only being about to deserialize data from the same version of Julia, hence it blocked supporting running multiple Julia versions in our Quarto notebooks.

This PR vendors Malt.jl and adjusts some code to allow for starting up and sending data across different versions of julia. Instead of Serialization we use BSON for serialization which manages to work across versions for the limited kinds of data that QNR uses, basically just strings, arrays of uint8, namedtuples and numbers.

In addition this also implements what was discussed in #215 to throw more informative errors when the Julia version running and the julia_version field in a Manifest.toml file do not match, which can, if ignored, lead to hard to diagnose errors on notebook startup. We now throw a hard error when there is a mismatch, and guide the user to a solution by either picking a different Juliaup channel, or re-resolving the manifest file.

---

Take 2 of #230.

[codecov]

Codecov Report

Attention: Patch coverage is 22.10928% with 613 lines in your changes missing coverage. Please review.

Project coverage is 31.05%. Comparing base (ad04a34) to head (a27d9f7).

Files with missing lines	Patch %	Lines
...rtoNotebookWorker/src/vendor/BSON/src/anonymous.jl	0.00%	135 Missing ⚠️
...toNotebookWorker/src/vendor/BSON/src/extensions.jl	0.00%	109 Missing ⚠️
src/Malt.jl	58.00%	97 Missing ⚠️
src/QuartoNotebookWorker/src/Malt.jl	0.00%	73 Missing ⚠️
...c/QuartoNotebookWorker/src/vendor/BSON/src/read.jl	0.00%	68 Missing ⚠️
.../QuartoNotebookWorker/src/vendor/BSON/src/write.jl	0.00%	59 Missing ⚠️
src/startup.jl	0.00%	20 Missing ⚠️
...rtoNotebookWorker/src/vendor/BSON/test/runtests.jl	0.00%	17 Missing ⚠️
...c/QuartoNotebookWorker/src/vendor/BSON/src/BSON.jl	0.00%	13 Missing ⚠️
src/QuartoNotebookWorker/src/render.jl	0.00%	8 Missing ⚠️
... and 4 more

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HEAD has 5 uploads less than BASE

Flag	BASE (ad04a34)	HEAD (a27d9f7)
	6	1

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #232      +/-   ##
==========================================
- Coverage   37.14%   31.05%   -6.10%     
==========================================
  Files          41       52      +11     
  Lines        1642     2389     +747     
==========================================
+ Hits          610      742     +132     
- Misses       1032     1647     +615     

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