Add --batch-compile to compile files of a library in one call

[ru551n]

Follow-up to #1235, and built on it. Only the commits after "Compile in parallel only with --parallel-compile" are new; the rest are #1235 and will drop out once it is merged.

Adds --batch-compile, which compiles the VHDL files of a library that are ready at the same time in one call to the compiler, instead of one call per file. Most of the time of compiling a file goes into starting the compiler and updating the library, so a clean compile gets several times faster. This is the automatic form of the soft file groups discussed in #1088: a clean compile batches, while an incremental compile of a few files compiles them one at a time. It can be used on its own or together with --parallel-compile.

What was added

• Batches: when the scheduler starts a file, it also takes the other waiting files of the same library whose dependencies are compiled, or are earlier in the batch. The files of a batch are passed in compile order.
• Which files are batched: only VHDL files whose compile commands are identical apart from the file name at the end, so files with different compile options, VHDL standards or libraries are compiled in separate calls. A simulator opts in with supports_batch_compile; GHDL, NVC and Riviera-PRO do. GHDL does not batch files compiled with coverage, whose .gcno files it moves one file at a time.
• Command length: NVC and Riviera-PRO read the file names of a batch from a file list (nvc -a @file, one name per line, and vcom -f file, quoted names), written to the output path and removed after the call. GHDL gets the file names in the command, because its response files handle neither quotes nor escapes, so a name with a space cannot be listed. A GHDL batch therefore ends before its command gets longer than 32,000 characters, below the 32,767 characters of a command line on Windows, and the remaining files go into the next batch. A file name a file list cannot hold, with a line break for NVC or a double quote for Riviera-PRO, makes its batch fail, so the batch is compiled one file at a time.
• Failures: a batch that fails is compiled again one file at a time, so the failing file is reported and its dependents are skipped as before. GHDL writes nothing for a batch that fails.
• Read rule: the library rule of Add --parallel-compile to compile files in parallel #1235 applies to every file of a batch.

Measured

A clean compile (--compile --clean) of hdl-modules, 330 files, wall time including VUnit's start-up, median of 3 runs:

	NVC	GHDL	Riviera-PRO*
one file at a time	5.99 s	7.37 s	11.83 s
--parallel-compile -p 16 (#1235)	1.65 s	5.97 s	7.49 s
--batch-compile	2.19 s	2.44 s	4.26 s
--batch-compile --parallel-compile -p 16	1.42 s	1.64 s	2.66 s

* With --keep-compiling, because hdl-modules does not compile completely with Riviera-PRO on master either ('latency attribute in sine_calculator.vhd). Every Riviera-PRO run compiled the same 327 files, failed the same 2 and skipped the same 2. The batch containing sine_calculator.vhd failed and was compiled again one file at a time, which exercises the fallback.

Every NVC and GHDL run compiled all 330 files. With both flags, GHDL goes from 7.37 s to 1.64 s, where --parallel-compile alone gives 5.97 s.

Tested

• New unit tests: files of a library compiled in one call, separate calls per library and per compile options, a failed batch compiled again one file at a time with its dependents skipped, and batches with --parallel-compile with and without concurrent compiles into a library. The last case covers a crash found while measuring, when a batch took a file the scheduler had not reached yet.
• Unit tests for splitting a batch at the command length limit, for a file list that keeps a batch in one call, and for Riviera-PRO's quoted file list with a name containing a space. With Riviera-PRO, a batch including quo"te.vhd fails and its three files then compile one at a time.
• Windows Riviera-PRO 2026.04 (under Wine): the VUnit uart example, copied to C:\fl\my proj, compiles all 147 files with and without --batch-compile, and with --parallel-compile -p 4, and its 6 tests pass after a batched compile.
• A UI test for --batch-compile.
• The unit and lint tests pass.
• GHDL stress test: 10 clean hdl-modules compiles with --batch-compile --parallel-compile -p 32 compiled all 330 files every time.

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