ACT-Backend v1.9

Changes since v1.8, how a compile ends and what it writes:

• Reported a dropped candidate with the allocator's reason (#144)
• Ended a compile that finds no assembly with status 1 and one line on stderr (#146)
• Prepared the output path first and wrote the output only when complete (#150)
• Named every limit of a compile and reported which one ended it (#153)
• Exited 1 when a required flag is missing (#155)
• Made an unreadable kernel end the compile with the no-assembly line (#157)
• Read each kernel attribute by name and refused what the reader cannot read (#163)
• Made a strided slice or clashing shapes end the compile with the no-assembly line (#166)
• Read a kernel's root from its ROOT mark (#168)
• Made a kernel line the reader cannot split end the compile with the no-assembly line (#170)
• Extracted the last e-graph after the iteration limit (#172)
• Kept the log directory private to its compile and out of the assembly's header (#177)
• Printed the search's progress only under --verbose (#179)

This release:

• The version is 1.9 in pyproject.toml, in act_backend/__init__.py and in the README's install line, and 1.9.0 in the generated crate's Cargo.toml and Cargo.lock.
• A compile that finds no assembly, including one with an unreadable kernel or a failing cost model, ends with one line on stderr that says why, exits with status 1 as a usage error does, and leaves no output.
• The usage errors and that line are lowercase after Error:, with no final period.
• A usage error leaves an earlier output untouched, and an output path or log directory that the backend cannot write ends the compile before its search.
• A compile prints on stdout only the candidates it drops unless given --verbose, and ends its search after one second, or sooner once the time since the start exceeds ten times the time of its best candidate; its no-assembly line says which limit ended it.
• The kernel reader reads each attribute by name, the root from its ROOT mark, and a rank-0 value as one element, declared as () in the assembly, and it ends the compile with a message naming anything it cannot read.
• A compile given no --log keeps its candidates in its own directory, which it leaves in place, and one given --log writes into that directory and removes nothing in it.
• The assembly's header names the kernel's path.
• The two examples compile attention.hlo to the same assembly as in v1.8, except for the header's # Input file: line.
• Its 324 tests run against the installed wheel in devanshdvj/act-env:py3.14-jax0.11.2 with TAIDL-TO v2.6, on amd64 and arm64.