Enable eight previously-ignored ruff lint rules

[mmacferrin]

First pass at trimming the [tool.ruff.lint] ignore list in pyproject.toml, per #40. This removes eight rules from the ignore list and fixes every error they raise. The ignore list goes from 138 to 130 entries.

Rules were chosen by running ruff check src --extend-select ALL --statistics to get the real violation count behind each ignored rule, then picking the ones whose fixes are mechanical and carry no behavior change.

Rules enabled

Commit	Rule	Change
b61771e	C408 unnecessary-collection-call	20 dict(...) calls rewritten as dict literals
b61771e	TRY201 verbose-raise	5 raise e inside except blocks replaced with bare raise, plus the 5 now-unused as e bindings that F841 flagged as a result
4d3f9fe	RSE102 unnecessary-paren-on-raise-exception	2 raise click.Abort() → raise click.Abort
2c2fa15	SIM101 duplicate-isinstance-call	2 isinstance(x, A) or isinstance(x, B) pairs merged into tuple form
a682718	FURB110 if-exp-instead-of-or-operator	2 os.path.dirname(x) if os.path.dirname(x) else "." → os.path.dirname(x) or ".", which also avoids calling dirname twice
56a6897	RUF005 collection-literal-concatenation	2 sequence concatenations rewritten as unpacking
c657d63	UP030 format-literals	5 str.format() calls in validate_dem.py switched from explicit positional indices to implicit ones
3d2e7c2	EXE001 shebang-not-executable	7 vestigial shebang lines removed

Notes

EXE001 — the seven affected modules are not executed directly: the package installs a single ivert console script (ivert = "ivert.cli:ivert_cli"), and everything else is imported or run through the interpreter. Removing the shebangs keeps all file modes at 644 rather than adding execute bits to library modules. It also retires the #!python3 line in utils/split_dem.py, which was not a valid interpreter path and would have failed if the file were ever executed directly.

SIM101 — the datetime check in icesat2_database_v2.py is kept as isinstance(date, (datetime.datetime, datetime.date)). Since datetime.datetime subclasses datetime.date, the second member is technically redundant, but preserving it keeps this a pure lint fix rather than a semantic one.

B905 (zip-without-explicit-strict, 15 sites) was considered and deliberately left out. Unlike the rules above it is not mechanical — each call site needs a decision about whether the zipped iterables are guaranteed equal-length, and strict=True converts today's silent truncation into a ValueError. That deserves its own pass.

Verification

• ruff check src and ruff format --check src pass, and prek run --all-files passes, at every commit in the branch.
• ivert --help runs, and all touched modules import cleanly. Two modules could only be checked with py_compile for environment reasons unrelated to this branch: validate_dem.py needs transformez, which is not installed locally, and plot_results_slope_centrality.py imports a nonexistent import_parent_dir module (pre-existing on main, confirmed by checking out main and reproducing the same failure).
• Module docstrings confirmed intact after the shebang removals.
• The rewritten .format() calls and unpacking expressions were spot-checked to produce identical output.

pytest is not installed in the local environment, so the test suite was not run.

Remaining work

This is one step toward #40, not the whole thing. The largest remaining block is the PTH* cluster (~380 hits across 20 rules), which is a genuine os.path → pathlib refactor rather than a sweep. Other sizable groups still ignored include ANN*, ERA001, E501, T201, and EM101/EM102.

Part of #40.