Rustify engine_bibtex - Part 4, the last of it

[CraftSpider]

This builds on #1077, converting aux and bst code. Opening to get tectonic-on-arxiv runs going, I'm slightly dubious that get_bib_command_or_entry_and_process is perfect yet, it's a really messed-up function.

[codecov]

Codecov Report

Merging #1083 (93a4126) into master (4b6c433) will decrease coverage by 0.04%.
Report is 10 commits behind head on master.
The diff coverage is 66.41%.

❗ Current head 93a4126 differs from pull request most recent head 05efe9d. Consider uploading reports for the commit 05efe9d to get more accurate results

@@            Coverage Diff             @@
##           master    #1083      +/-   ##
==========================================
- Coverage   46.27%   46.24%   -0.04%     
==========================================
  Files         171      171              
  Lines       65031    65038       +7     
==========================================
- Hits        30093    30076      -17     
- Misses      34938    34962      +24     

Files	Coverage Δ
crates/engine_bibtex/src/buffer.rs	77.58% <ø> (ø)
crates/engine_bibtex/src/char_info.rs	100.00% <100.00%> (ø)
crates/engine_bibtex/src/hash.rs	63.52% <100.00%> (ø)
crates/engine_bibtex/src/other.rs	94.33% <100.00%> (ø)
crates/engine_bibtex/src/pool.rs	82.95% <100.00%> (ø)
crates/engine_bibtex/src/xbuf.rs	51.42% <ø> (ø)
...xetex_layout/layout/xetex-XeTeXLayoutInterface.cpp	30.66% <ø> (ø)
crates/engine_bibtex/src/global.rs	83.33% <90.00%> (ø)
crates/engine_bibtex/src/peekable.rs	84.61% <88.23%> (ø)
crates/engine_xetex/xetex/xetex-engine-interface.c	81.81% <0.00%> (-8.19%)	⬇️
... and 10 more

... and 30 files with indirect coverage changes

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[pkgw]

I have taken the liberty of rebasing your current branch to the new master, fixing the cargo fmt complaints, and fixing up the harfbuzz sub-repository version, which accidentally rolled back from 8.1.1 in #1077.

[CraftSpider]

Awesome, thank you. There may be a slight delay on the final commits - I got a bit ambitious, tried to do too much in one commit, and need to rollback and re-try. Frustrating, but better to accept it and start again then keep playing whack-a-mole with like 200 lifetime errors.

[pkgw]

@CraftSpider FYI, I'm hoping to put out a new release soon, so that people can try the new Linux aarch64 builds and Linux binaries that link against OpenSSL 3 (#1092). But it's really easy for me to roll releases with the automation we have using Cranko, so don't worry, I'll make another release promptly whenever this PR gets merged!

[CraftSpider]

There are infinite cleanups I could do, but this should be ready and those can come later. This rips out all remaining C code, and does some basic cleanup on the resulting crate, though it's still very obviously ported code still.

[pkgw]

Sorry for letting this linger so long! I've been trying to pare down my GitHub backlog the past few weeks and somehow it keeps getting bigger :-/ I haven't lost track of this, though.

[pkgw]

Argh, very sorry for taking so long. Rather than letting this keep on sitting as I try to find the time to give it the review it deserves, at this point I'm just going to go ahead and merge. Thank you for all of your work on this project!